Hey SpreadingSmiles
I haven't had any interviews yet, but I guess the following general tips are good for any interview. Relax, be confident (but definitely not arrogant), be yourself, be honest, polite and enthusiastic and friendly. If they ask you something you don't know, just say so instead of bluffing because if they catch you bluffing, that is worse than saying, "I'm sorry, I don't know". Answer the interviewers' questions concisely and accurately and not in a 'beating-around-the-bush' style. Try to make eye contacts with the interviewers when you listen to the questions being asked and when you answer them.
It will be good if you have some knowledge about their program and school in general. Think of questions to ask them before you go, if you can. Hope that helps.
All the best with your interview.