My advice is dress nice, research the company a bit so you can ask questions about it, and project a mein of confidence. Even if you are scared, smile and make eye contact with your interviewer. Give a firm handshake and be sure to ask questions about the job at the end - that shows interest.
Probably the best thing you can do is pump yourself up before the interview. Before an athelete runs or an actor goes on stage, they "pump up", and their pre-performace jitters go away because of adrenaline. Do the same before your interview. Don't go in scared, go in feeling like you own the place!