It sounds like you're wondering what to expect, since you haven't had a med school interview yet.
I think the preparation will be similar for both (know your application in and out esp. the activities, be able to talk about yourself), but you'll have to educate and remind yourself about the specifics of each of the schools (mission statements, curriculum, what makes each unique that you can comment or ask about, how do you fit into each school). If you do the prep in advance, it'll be easy to remind yourself of it the days leading upto, and the day of the interview.
Not a bad position to be in! Make sure you debrief after the interview with a trusted advisor (friend, current med student, parent, whoever) about how the interview went and what you think you did well/could improve upon. That way, you'll be even more amazing that 2nd interview. Get sleep, eat, and use the bathroom beforehand so you're where you need to be when it's time to sit down & chat!
Hope that helps.
-current resident physician