I interviewed there last year...and got rejected. It doesn't matter when you interview (unless it's for early decision) because they don't make any acceptance decisions until the following March--which really sucks. Plan on a long day for the interview (~8am-4 or 5pm). My hour interview with a student was really relaxed and informal. In the hour with the faculty member, she made a big ugly frown face

after each of my responses and she said "whatever"

really sarcastically when I said that I wanted to be a primary care physician. You also meet with the Dean or Assistant Dean of Admissions one-on-one for 15-30min....nice tour of facilities...lunch with 1st or 2nd years...
As far as suggestions go, the student and Dean will always be low stress interviews. They are more interested in talking about you rather than grilling you on healthcare issues. If you get someone like I did for the faculty interview, don't let their attitude get to you because they are probably just testing your character and want to see how you respond to stress. I'm sure most of them are much friendlier than who I got stuck with. Don't worry about it being your 1st interview because generally people are actually most pleased with their performance during their 1st time and then it goes downhill from there.