How does one master an interview?

The simple answer is: practice makes perfect. The more you do it the better you become at it. Know your subject, know yourself, your skills and what you are good at. Be able to explain it and provide specific examples to support those claims. Think of specific situations that you can talk about when asked about your strengths and weaknesses, how did you handle the situation, what did you do, what was the outcome etc. And try to be yourself, practice how to stay calm under pressure and control your nerves. You can stand in front of the mirror and practice. Or use your phone and record yourself speaking, you will see where you need to improve and control your body language as well.

It's all about preparation and some confidence. Remember, we are all our own worse critics. So the more you practice, and you know you did practice, it will give you the peace of mind and confidence you need. You will feel ready.

Good luck!

Great advice from Agata to be yourself. The worst approach is to memorize and try to think of what an interviewer WANTS to hear from you. Trust me, they have heard everything and can tell a fake reply from one that is spoken from the heart. It definitely helps to go through some common questions and think about how you would answer. There is a website " collegeapp.about.com" that list 15-20 of the more common possible questions you might be asked. Don't think you have to make some profound statements, sometimes speaking simply, prepared but not like you wrote a speech and memorized it, can open the door to some great interaction with your interviewer.
Try to relax and look your interviewer in the eye. Be respectful, don't be afraid to use some humor, just don't turn into a comic or use a lot of slang expressions. Don't come off as bragging, even if your accomplishments are outstanding, simply state what you have done with tempered pride. Question about your personal attributes can be unnerving, but be truthful. And don't try to take a positive and make it a negative like "Oh, people tell me I'm just too friendly". That never goes over well.
All interviewers, whether for college or in the working world, appreciate honesty and being spoken to as if in conversation, not rehearsed responses. So practice and remember to SMILE.