Whenever you present yourself in a truly important situation, you are going to experience some nervousness. The real issue is to learn to control it, rather than letting it control you.
In order to remove the pre-interview jitters, you need to remove as much of the unknown as possible. One key way to do this is to anticipate the interviewer's questions. Obviously you cannot predict all of them, but you can figure that you will be asked to describe the responsibilities of each of your recent positions, what you liked most, what you liked least, your major accomplishments, reasons for leaving, personal strengths and weakness, and your near-term and longer term objectives. At the same time, make sure that you have some good questions to ask.
You should also go through some practice interview sessions with a friend who can provide an honest critique. And, before you start any real interview, take a few deep breaths, tell yourself to relax, and then give yourself a brief positive message, such as, "This will be a great interview."
As a side note, no matter how nervous you are, don't forget about the interviewer. In this tight labor market, he or she might be nervous too. In fact, minutes before the interview, the interviewer may be uttering the same positive message as you.
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