This will vary greatly depending on the postbac program. In fact, just a couple of days ago I (BM) had a discussion with drizz (Scripps) over the efficacy and appropriateness of medical ethics questions in postbac interviews.
As far as the basics go, yes, wear a suit or whatever else seems appropriately formal -- treat it like a medical school interview. The atmosphere is only as tense as you are, and most of the questions will center around the classic "Why medicine, why now?" query. You need to have clear answers to any derivation of a question regarding why you chose your original career path, why you chose to switch to medicine (hating your current job is the WRONG ANSWER) and what your expectations are for medicine.
Avoid sounding foolishly optimistic or hopelessly ignorant. Try to convey that while you're excited to get started, you understand it's going to be challenging from Day 1 and you'll have ups and downs. Some things will come easier than others, but you're educated enough about this career path to be certain that the motivation of achieving its end goal is enough to sustain you.
You'll be asked what you think the biggest challenge will be and how'll you handle it. This could be a particular course, or perhaps the MCAT, or maybe something more personal. What your answer is isn't important -- how you answer it (and how your answer displays your maturity) means everything.
Have a clear vision down the road, but be open-minded. Put some thought into what kind of medicine you'd like to practice and in what setting, but don't claim to have your career planned out because, let's face it, you don't. Read the science section of a decent newspaper for a few days prior to interviewing, review competing healthcare system proposals and know a few unique things about your postbac and its college -- drop some of those tidbits when you interview and everyone takes notice. But be subtle -- otherwise you'll look like a ass clown.
If you've made it to the interview, you've already passed through the initial cut-off. As such, don't dwell on your accomplishments -- your interviewer already knows them, trust me. Rather, show what can't be shown on paper -- that you're intellectual, mature, congenial, honest and genuine. If you happen to be charming and funny, too, that's just icing on the cake.
Interviews are subjective and that scares some people, but I would encourage you to think of it as an opportunity. Turn on your A-game for 30 minutes and you've just put yourself above every other candidate -- something a paper application can almost never do.
All the best.
xf
