I'm looking for two things from med students: preparedness and enthusiasm.
You can never over prepare, but you can over annoy. The only way I was ever annoyed was by upstaging. NEVER try to make someone else look bad. You should always look to make the jr residents look good and their job is to make the sr residents look good and their job is to make the attendings look good. I know it sounds counter-intuitive, but if you make the juniors look good, you will ultimately shine. For knowledge, all a student needs to know is the anatomy. You HAVE to know the anatomy. If you can know the indications for surgery and maybe a bit about the complications, you're golden. All else is just icing.