I agree with Kris about the breath mints and tissues! (Gum does not work - no where to put it). Other good "hints" are to make sure your hands are warm (rather than sweaty or cold), so that when you shake the person's hand, they don't focus on or remember the handshake, and to check your appearence in a bathroom before you go to interview (looking for food in teeth, as kris said, that your clothes are straight, etc). Other than that, make sure to read a lot about the school - so you can answer daredevil's question - and so you can ask good questions of the interviewer. Read the school's brochure or web site, and MSAR entry (these are written by the med schools) and be familiar with your personal statement, secondary answers and, dare I say, AMCAS application. Try to get to "meeting place" at the school at least 30 mins early (in case something happens) and make sure you do whatever you can to be alert, happy and ready (e.g., coffee, good breakfast, music, whatever). Try to get a good night's rest and to not worry too much. Make continuing eye contact with your interviewer. Do not get psyched out by any other interviewees and their "stats" or experience (you're all pretty much on the same level at this point). The more you can avoid talking to really stressed out people, the better for you mentally. (I cannot recall this being an issue at many places I interviewed -- most applicants were really nice and supportive.)
In the end, other than logistical things (like getting there), a good interview occurs when you are relaxed. The best way to achieve that is to realize and believe that you are very deserving of a spot at the school (you wouldn't be interviewing otherwise) - it seems that once you believe that, you relax more and are better able to carry on a "normal" conversation. It can actually become fun to interview - if you decide to look at it in this way. Good luck!
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