I learned almost everything I know about crit from my Sophomore Design Professor, Willy Schwenzfeier. He was kind enough to let me share the rules we used in class to make crit days enjoyable—for both presenter and audience:

Don't Pat Yourself On the Back
The whole point of a critique is to make your work better and to make you a better designer—not to prove or validate what a great job you did. Of course, it's nice if you did do a great job, but there's always something to be learned to make your work better.

Keep Your Presentation Short
You should be able to distill all the important information you need to get your project across to your audience down to two minutes. Keep things brief and succinct, or you will lose people's attention. Keeping things short also leaves more time for constructive feedback.

Practice What You're Going to Say
Rehearse your intro until you can say it in your sleep. Starting off strong will set the tone of your presentation, and it will help if you get a wave of stage fright when you get in front of your audience. You don't need to have a word for word script for your whole presentation, but at least take note of your main points and the order you want to say them. Get some friends together and go through a test run to make sure the volume and speed that you're talking at is understandable.

Don't Get Defensive (Shut Up and Listen)
Feedback from others is a gift. Someone is putting effort into helping you. Accept that goodwill with grace, and reinvest that energy in your work. That's why being quiet and listening is so important. No one wants to hear you scramble to justify yourself. You had your chance to frame/position your work with your presentation. Now it's time to take in what others thought.

You Don't Have to Take People's Advice
Just like in user research, you're not supposed do what the subjects of your research say. You are supposed to deduce WHY they said what they did and figure out if you can devise a way so they don't need to say that again in the future. Same with critiques, especially the early on ones: What's driving this concern? How can you alleviate it? Should you alleviate it?

Don't Waste Time Answering Questions
You have a limited amount of time to get feedback. Acknowledge the question ("Oh, interesting, I'll have to think about that…") and then try to garner more of the same from the others. Some kinds of questions from the audience are good: if they're probing more deeply into your ideas, etc that can be a great sign that you've got something worth chewing on. If the questions are about clarifying the very basics of your proposal, oooof, something's not right with either your concept itself or the way you shared it. But there are lessons to be learned even in that: Where'd you go wrong?

When Feedback Gets Off Topic
If someone is saying things that do not exactly align with what you meant, you could probably still learn something. I mean, they're still saying it in reaction to your presentation/work so there's probably some kind of link. Serendipity might lead you somewhere…

I guess the unofficial final tip is to have fun and let your passion for your design show. If you look bored or disappointed up there, it's going to affect how people see your work. Don't sell yourself short.