worst thing you can do is overthink. i know, easier said than done
unlike other aspects of your application (GPA, MCAT...), studying ahead doesn't really translate well for interview prep. the only "studying" you can really do is to do some research on each school you're interviewing at so that you can ask a couple intelligent questions of your interviewers. they like to know you're considering a potential offer from them seriously, so at a bare minimum spend an hour trolling the school's website.
other than that, it's a safe idea to prepare an opinion (but *not* memorizing a monologue!) about modern US healthcare, ethical situations (hipaa laws, counseling a patient, or even working with a difficult colleague), and the like. then, once you have a position on those, march into your pre-health advisor's office and ask them to toss some tough questions your way, without telling them what you've been prepping for. both of the advisors i practiced with happened to be former Ad Com member at a very difficult-to-get-into MD program, and the questions they proposed were about 20x more difficult to answer than the actual questions i got during any of my interviews. those mock interviews showed me that i had a very poor surprise response, so i realized that i had to take a deep breath after each question to regroup instead of blubbering out a confused answer. and yeah, those mocks are very different and more real than having a parent/friend/professor/boss practice with you.
really, that's all the prep you should *have* to do - try not to fidget, don't keep a checklist in your head about topics you need to cover when you're in there. if you get a chance to just yak with your interviewers, it's really just important to show that you've been listening to what they've told you and that you think before you speak. that's tough to do if you've crammed your head full of 100 pages of interview advice... and yeah, i know i'm getting pretty close to a full page myself
be yourself, wear a suit that makes you feel confident and not fidgety, smile, and they'll be able to imagine you sitting bedside with their grandma - an instant way to almost guarantee a spot in their next class.