Undergraduate degrees can feel very intense, and are often a challenging experience. Each major has dreaded classes (in geology, structural, stress and deformation, crystallography- all heavily math-oriented classes- are often considered the killers, though for me mineralogy was the nadir- more on that another time). But the fact is, you are being told specifically what to learn and how to learn it. Graduate level degrees go far beyond that. At the master's level, you need to become proficient- not just comfortable with, but good at- pulling meaning from the professional literature. You also need to develop a healthy skepticism of it- that is, an ability to recognize what is not being addressed, alternative explanations, counterarguments against the proffered explanation of the data, and so on. In other words, not just mindless nay-saying, but an ability to take an intelligent contrary position. Every author is first and foremost a human being- we want to be right, and it's difficult to recognize flaws in our own reasoning. Science as a discipline has institutionalized a counter to this- each of us is expected to critique without mercy. That does not imply viciousness or antipathy (though sadly that does work its way in from time to time), but it does mean that concern over "feelings" is not part of the consideration. If you spot a flaw, you identify it.
To someone who is not ready for it- that is, a person whose experience is mostly at the undergrad level- this can be intensely painful. So the first bit of advice would be, "Keep in mind that it's not meant to be personal (especially if you don't have professional rivals), and don't take it that way."
At the undergrad level, most of the reading and other sources you use will be basic materials that are familiar to your professors. As you move into the masters level, you start to spend time with speciality sources that are not as familiar to the discipline as a whole. So, for example, recent articles on magmatic petrogenesis are not going to be familiar to the department geowhizzics guy, nor the petroleum engineer, though both will be familiar with Bowen's reaction series. As an undergrad, one typically will have an advisor in the department, but it doesn't much matter who. At the Masters and PhD level, a student needs to have someone who is pretty darned good in the area in which the student is working. That is not so much because the student will learn most of the curriculum from that advisor/mentor, but because that mentor knows what resources to point the student toward.
The second bit of advice: At the BS level, your professors are mostly responsible for telling you what you need to learn. At the graduate level, you have to take that responsibility on. Your advisor should be able to help, but YOU need to figure out what you need to learn- then learn it.
Next, at the undergraduate level, the idea of "socializing" brings to mind drinking beer, music, dancing, and other aspects of bacchanalia. At the graduate level, socializing may involve any of that, but almost certainly also involves discussing what you're doing, interesting material you've read or thought about recently, what your area of interest is- in other words, a great deal of discussion of professional interests. To someone outside of science this probably sounds horrible, but the fact is, if you've gone on to an advanced degree, it better be because you love the subject- otherwise you're going to lose motivation at some point. If you do love your subject, the opportunity to pick the brain of someone who knows as much as you do- maybe more- in a social situation is pure gold. You can bounce ideas around- they may get knocked down, or they may not. You can engage in reckless speculation- something may come of it, or maybe not. But it's nonthreatening; you're not in front of an audience, trying (and investing serious emotional energy) to make a positive impression. It's in these unguarded, "pointless" social moments that most of the creative work in a discipline happens. This is why professional meetings are so very important- not the presentations, or the posters, but the partying that takes place afterwards, or the cup of coffee shared between sessions. The posters and presentations are important, but they're the result of two or a few smart people socializing. Some random thought gets fixed in someone's mind, and like a seed dropped into a super-saturated solution, a full blown idea crystallizes around the nucleus. Everything else is shaping, testing, polishing, retesting- then hopefully, communicating. All that other stuff, which occupies the vast bulk of our work lives, obscures the fact that it's the informal settings where we most often get that brief instant of inspiration. Social settings also provide a place where we can get and give criticism in a non-threatening, non-judgemental, and even fun, manner. At the very least, there's a good chance you'll get a "have you seen..." or "have you read..." sort of a comment. The astute student learns to follow up on these; the really sharp student learns to ask follow-up questions to judge whether it's going to be worthwhile following up on those sorts of recommendations.
So the third bit of advice is to learn how to use your colleagues and peers as sounding boards. I don't like that phrasing- the idea of "using" people is smelly to me. Let's say, "learn to use socializing with your professional peers as a source of mutual inspiration and feedback." Much better.
Finally, if most of the feedback you're getting says "you did OK," take it at face value. You almost certainly did fine. I know it stinks, I know it hurts, but we tend to be our own harshest judges. The positive aspect of that is that we do tend to put those self-judgements behind us with time.
As an undergraduate, I went to quite a number of seminars and defenses- I practice I recommend to all undergrads. (actually, I think it ought to be a requirement for undergrads to attend, let's say, a dozen over the course of their degree- that would amount to one a season for four years. Sound reasonable?) I've got three illustrative stories:
1) A student was working in some carbonates in eastern Nevada, looking primarily at Permian brachiopods. During his introduction, discussing the overall structural framework of the area, he briefly mentioned the Roberts Mountain thrust. The actual trace was nowhere near his area, and there was no apparent deformation in his area related to that fault, but he noted that some of the work implied that his rocks might have been exhumed after that thrust sheet was eroded off the area. As it happened, one of the profs in the audience had done a lot of work on that fault, and during the Q and A, wouldn't let it go. In one of the best parries I have ever seen, the student responded, basically, that he would review the literature, but that he wasn't certain he saw the relevance of the feature to what he was trying to study. Could (the prof) explain its relevance? End of discussion.
Lessons: a) Be aware of the professors' backgrounds- they do tend to pick up on and doggedly hang on to anything related to what they consider "their" area- another example of this next. A little bit of prep here can go a long way- just show you've done due diligence to something that they consider the center of the universe. If you can show you know a little they'll ask for more, but they'll be satisfied with a little. Obviously, if it really is relevant to your topic, you should know more than just a little. In this case, as best as I could tell, it really wasn't relevant. b) state that you'll follow up on it and read some more. Do follow up on it- in a later slack moment, go to the prof, and say "I was quite interested in your comments on (whatever), and I was wondering what you would recommend that I look at." This is quite shameless ego stroking, but it goes a long way. The fact is, these people are not just in charge of your degree, they're in charge of your future. You want to make them feel respected and valued. If you do, by and large, they'll return the favor. And sometimes their recommendations really are worth following. Sometimes they're just irrelevant. c) Be careful here, but politely asking someone to explain how their concerns are relevant to the study you've done can get them to back off. I say be careful because while no one knows everything, all disciplines have their canonical knowledge. An undergrad degree provides this to an extent- masters degrees are about learning how to use it. But each professional has a slightly different idea of what that "common knowledge" ought to be. It's fair to ask "how is that relevant," but a prof will definitely take umbrage if you seem to be implying that something he/she thinks everyone in the discipline ought to know is simply unimportant.
2) I don't remember the context here, because the Q and A was a train wreck I could never quite get out of my head. But the presenter mentioned "conodonts" in passing, and commented that some people thought they might be teeth. As it happened (wouldn't you know) one of the profs was a conodont guy and wouldn't let it go. I don't know how many times I heard the question "But are they teeth?" I could tell the student was shaken, and I never trusted that prof again. It seemed cruel and vicious and just mean. The prof should have let it go. What should the student have done? First, as a sophomore, I knew more about conodonts than he did. As I mentioned above, there is a set of common knowledge that everyone in the discipline should have. He didn't. My response then (and now- I haven't learned much more about them, except I think the most widely accepted idea is that they're structural elements of a chordate-like organism) would have been, "I know there's some studies that claim that they lack wear patterns that would indicate teeth, but I know others just keep going back to that idea. I think the best answer right now is that they most likely are not, but it's not completely out of the realm of possibility."
Lessons: a) patch any holes in your basic knowledge of your discipline. b) don't drop irrelevant comments into your presentations- they can blow up in your face. c) Never be afraid to say "I don't know." Especially if you don't. That's a tough one, and I don't know how to help, except to say with practice you learn to love it. It ends conflicts. It shuts down arguments. Above all it's an admission of opportunity- look back through some of my older science posts and see how excited and breathless I get when I use the phrase "I (or we) don't know." It's positively obscene, is what it is... but I do love that phrase. d) see lesson "a" in story "1."
3) A student was doing a survey map (i.e. not high detail, petrographic conclusions about geochem, but no detailed chemistry) in a mildly mineralized area punched through with about a dozen highly mineralized hydrothermal breccia pipes. A prof asked him about the nature of the clasts in the breccia. The student basically tried to blow him off. Turns out, he hadn't done any thin sections on the breccia clasts- he had looked at some of the interstitial material where most of the mineralization was located, but he hadn't really looked at the clasts at all. The professor got pretty aggressive- which I think in this case was justified, the student tried to play the "it's just not important" card again, and it escalated. I've never witnessed out-and-out screaming at a presentation (though I've heard it does happen), but this was getting close. Finally, the student sort seemed to come to his senses and realize he was not helping himself. It was a fairly large area at a decent elevation, which means field season is limited, There was a tremendous variety of rock, with the alteration/hydrothermal episode imposed on top of that, so it was a messy area. His support and time was limited, so he couldn't do everything he might have liked to. Finally, it just never occurred to him to do a few sections of the clasts (The insight into underlying rocks could have been useful, and I didn't have the sense he'd even taken a hand lens to them). Overall, it was one of the less impressive presentations I saw as an undergrad.
Lessons: a) Don't get hostile. Period. As a student, you lose. Even as a seasoned professional, it makes you look like an ass, and does nothing for your reputation. As a student, you lose. b) Always, always, always treat the faculty with respect. Especially the department Secretary. No joke. c) Don't overlook the obvious. As I implied above, I do think that happened here. d) Don't confuse "reasons" with "excuses." I think that happened here as well, but if the student had started with the "reasons" he basically ignored the breccia clasts, rather than first trying to dismiss the question, then escalating into hostility, then finally tucking tail and whining like a whipped dog, I would remember this very, very, differently- a weak, but nevertheless interesting discussion of an area where I've spent a fair amount of time. Rather than a disaster narrowly averted. e) Cultivate a healthy curiosity- I don't know how he could have paid so much attention to the ground mass and ignored the clasts- they're altered like crazy, but they're clearly some sort of intermediate volcanic material- not rhyolite, not basalt, definitely volcanic. If he could have said just that much...
Now here's the punchline: all three of these were master's defenses, and all three passed.
I've spent way too much time on this, but here's a few other generalities for surviving grad school:
- Don't let it get you down. You'll have good days and bad days, that's life. If all the days start feeling like bad days, hie thee to a doctor. Stress can trigger depression, which is a seriously life-threatening disease. Take my word on that.
- Explicitly: foster positive relations with everyone in your department, faculty, staff, grad students, undergrad students. As you work on a project, take breaks from time to time, wander around and talk about it to others. "What am I missing?" "This was an interesting thing..." and so on. Show through your social interactions that you are welcoming others to think about (maybe help with or criticize) your stuff. They'll like you for it, they'll appreciate your enthusiasm, and they're likely to be surprisingly helpful. They're also likely to be more considerate in seminars and presentations.
- Do understand that ideas are only accepted in science after they've been brutally examined and cross-examined. This is a reality. Given our nature, it's difficult for us to separate our ideas from our selves, but they really are different things. When your idea or statement is being questioned or attacked try to keep this in mind. It makes it much easier to accept "constructive criticism." It still hurts, but not as much.
- Have faith in yourself. Know that you will get through. Know that your ideas and thoughts might be improved- nothing is perfect- but "room for improvement" does not equal "bad."
- Set aside time for yourself. This is specifically time for you to be happy. Nothing else. For me, that was mental permission to read for pleasure for a few minutes each night, and Friday Night Burgers and a pitcher of diet coke for a couple hours each week. Not much, but for the first four or five months of my masters program, I wasn't giving myself even that. Want to talk about a squirrelly SOB...
- Get enough sleep. 'Nuff said.
- Understand from the outset that an MS is not just a continuation of undergrad schooling. It represents a whole new level of taking responsibility for yourself, your learning and your life. I get very prickly about those who derrogate higher education, but many undergrads don't really use the experience to develop adult habits- I know I didn't. A graduate degree requires that you develop such habits, and quick.
They found our camp that evening, and came over to visit. And it was clear from the outset, they were good friends, each really enjoyed the other's company. Want to talk about cognitive dissonance...
Finally someone had the presence of mind to actually ask what we were all thinking, basically, WTF? I have never forgotten their response. In essence, They really didn't agree on how to interpret much of what they were seeing. They didn't see eye-to-eye on much of anything beyond the basics with respect to the geology. But neither thought there was anyone else out there that they trusted as much as the other to challenge them. Their language was partly game, partly social signal (I think a polite smile and nod of agreement would have been interpreted as smug, condescending, and a message that the comment wasn't worth responding to) and partly a gimmick to trigger free, rapid-fire thinking and response. They weren't even really aware of it, since they'd been working together off and on for nearly (at that point) three decades.
So the point is, having your ideas challenged is not only part of the game, but eventually (even if it doesn't feel like it now) it's a part of the game you'll come to value and appreciate. And you'll seek out those who can do it best.
Good luck.
From 
Update: Yet another addition, 
Last update: Anything else I'll put in a new post. Promise. This video puts the above moment in a more understandable context. A little more.
'Cesco's warped humor has been growing on me rapidly, and today's comic was all it took to motivate me. In the RSS reader, there is a note that "Joe" 
Conservatism used to stand for some things I can support- such as keeping expenditures down, and balancing the budget. Such as the idea of everyone equal under the eyes of the law. Such as minimizing the government's interference with adults making decisions for themselves. Such as going with tried and true solutions when those look like they'd work best. But my adult life has seen a refutation of every one of these principles. And I blame, first and foremost, the religious right. The idea that God hates everyone who doesn't believe what I believe. The idea that those who Jesus loves, prosper- and by extension, why if someone is prosperous, then Jesus loves 'em. That if God has forgiven you, everyone else should too. The idea that the US was, in its inception, a Christian Nation- no, a Protestant Nation, no a Southern Baptist Nation. Narrow it down, exclude, divide, find more things and people that God hates, hates, hates.