Interviews can be very intimidating, so do whatever you can to lower your stress. Get a good night's sleep. Arrive at the interview location at least fifteen minutes early so that you don't have to be in a rush and worry about being late. Even taking a simple ten minute walk before you go can help.
Doing the little things well to get ready for a job interview can be the difference between you getting the job or not. Do these simple things and you will already have an advantage over most of the competition.