As the subject states, I probably don't know any more about interviewing than the rest of you, but now that I'm almost through my app season and just completed a couple of interviews, I thought I'd give my tips. Maybe I should have waited to see if I get accepted anywhere, but I wanted to write while things were fresh in my head.

I don't hope to be as helpful as the illustrious rhyme, but maybe people can add their tips here and then we can merge them in with that thread later.
1) Some people are going to disagree with me, but if you have a chance to interview with an adcom, take it. These are trained professionals that generally have years of experience interviewing people. They will put you at ease - they're likely to smile and agree even if you talk about how you ran over your neighbor's dog. This will make you more confident, which is a huge part of the interview. You have no idea what you're going to get with a student or alum.
2) Have a few different leadership and teamwork stories available that show different qualities. You don't want to be thinking, crap, I've used up my leadership story on this question and I know there's another leadership question lurking behind it.
3) Practice out loud. I found that I say obviously a lot, even when I'm explaining things that the interviewer can't possibly know about. For some reason, I don't say it in my head.
4) If you can't answer a question, make sure you can answer it for the next one, chances are you'll get a similar one.
5) If you have the opportunity to interview at one of your lesser choices first, try. It will be a chance to get the nerves out and know which things you need to improve upon.
6) One thing that I did that I found helpful was to take what I considered the five main themes - walk me through your resume, why mba/goals, why this school, leadership, and teamwork and just jot down scratch notes/bullet points of things to mention. Then I would read through it, but answer in my head. This way I memorized the main points, but wasn't trying to memorize a script. For Kellogg, I did also tape record a sample interview that I could listen to on the day of while driving there. Then I also had some spare time before my interview, so I wrote down all the points that I planned to make from memory so that I could make sure I knew them all.
That is all I can think of now, I will update if I remember more.