HI! I interviewed last year. To prepare, I thought of answers to all of the questions that my undergrad pre-med advisor gave us in a packet. I also came up with questions I had for the school (what opportunities are there for clerkships abroad? flexibility in curriculum? student life?) and did thorough research on the web about the schools program.
Finally, on the day of the interview (or the night before) I re-read my application to remind myself of the points I wanted to make.
Thats what i did. Sounds like a lot but it gave me a lot of confidence on interview day and was well worth it!! Good luck!!