Think of the interview as just a friendly conversation with another person. Try not to think about the outcome. I tell myself before every interview that I don't care if I get the job and I am only there to have a good talk about working there possibly some day. For me, having that attitude takes pressure off myself and I can be myself.

I also realized that many times the people interviewing you are uncomfortable doing interviews and are a little nervous too. I had to interview people as part of my last job so I know that from experience.