As far as preparing goes, check out the school's website and make sure you understand their program and things that seem important in their curriculum. I think its always beneficial to know as much as you can about a school before interviewing.
Like DHG said, relax X3! Be yourself and if you have a good personality, let it shine through. Interviews are important in that they like to make sure you can communicate and that there is more to you than just high numbers on a piece of paper.