Research the schools which are interviewing you. Re-read your personal comments essay, and supplemental question answers. Make sure you arrive on time. If you are delayed, call the Admissions Office to explain. Present yourself openly and honestly.
Medical schools have room for different kinds of people.
Some candidates come across as more passionate, while others come across as more calm. Some are more decisive, while others are more thoughtful. Try to stay in the moment, and attend to your interviewers and their questions. It is normal to be a little nervous, and for some questions to unbalance you. Put your best qualities forward.