Also, check out the studentdoc forums for the interview forums...people usually post questions that they have encountered for your particular school. Those questions are really helpful, so be sure you can respond naturally to all of those questions.
In addition to all the great advice above, think about good questions that you can ask the interviewer. Do your research; if you happen to know your interviewer's name, see if you can find out anything that you can make a connection with. When i went to interview for Maryland, I perused all the bios of the faculty members while i was on my flight there...lucky for me, I hit the jackpot and I remembered something that my faculty interviewer was involved in. It goes a long way if you can show you're just as invested in the interviewer and the school as they are in you. Ask them questions that make them feel you're SERIOUS about attending that particular institution (i.e., location, transportation, availability of internships, etc.etc.) You want them to know that you are going there because their institution is special, not because you're desperate (regardless of your true feelings =P).
Most importantly, remember this: the interview isn't out to "GET" you. They're there to find out more about you. You've already PASSED the first round by getting to the interview. Now it's all about impressing them and demonstrating to them why you deserve to go there instead of the other 6 people. Talk about yourself; don't assume that because it's on your resume that they'll have read it. Don't be too upfront and tight, but at the same time, make sure they know that you know your strengths, you know your weaknesses, and you know how to play your cards so that you are a valued addition to their community.
