I have 2 coming up, and although I am a little bit nervous I'm trying not to be. Don't be nervous! After all, you're going to be talking to someone about the career you have chosen, it should be pretty second nature.
Like said above, just be confident, be sincere. Don't make up answers or tell them what you think they want to hear, be honest. Making eye contact is very important. Also, do your research about the school before your interview (although I'm assuming you have done this extensively). They will probably ask you why you like their school, why you would like to go there over the rest, why you chose to apply there, etc.