The interviews are pretty relaxed and in fact, I felt like my interviewer spent more time talking than I did (so much so that sometimes he asked questions and immediately answered his own question, and I just gave my input afterwards). Of course, your interviewer might not be like that, but I think the general consensus from everyone is that it's pretty laid back and conversational.
If anything, just know why you would pick Medical College of Georgia to go to medical school and figure out why it would be a good fit for you, especially if you are out of state like I am. Also, if they give you an opportunity to ask questions about the school/campus, try to think of questions that you actually want to ask, not cookie cutter questions about the curriculum or anything else you could answer by looking online.
Other than that, relax, take your time answering questions, and just enjoy the campus!