for orientation or on a normal day?
orientation - dress basically like you did for interviews, maybe a little more relaxed but still business-casual.
normal day/no clinic - basically anything you want within reason. don't wear sweatpants or any tshirts with offensive slogans, don't come in in a cape or something wierd like that, but use good judgement and look around at what others are wearing and you'll be fine. on average most guys wear jeans or khakis and a collared shirt or a tshirt. once you get your scrubs a lot of people just wear those.
if you're scheduled to be up in clinic, you'll need to be wearing either scrubs or nice pants (no jeans or shorts) and closed shoes (no sandals). shirts can be pretty much anything since you'll have your coat on anyway, but words can show through the coat so no offensive slogans. the dress code is taken a lot more seriously in clinic than down in the classrooms, and you WILL get taken aside if they see something they don't like, so definitly be on your best behavior up there 🙂
if you do a search for 'michigan' i know there are some old posts that might answer any other questions you might have 🙂