As you've posted this under aromatherapy, I guess you are looking for oils that will help and there are plenty (for example, you might try burning frankincense beforehand, or putting lavender on your pillow the night before to make sure you get a good night's sleep).
But really the best way to overcome interview nerves is to feel confident you can answer any questions you might be asked. So think in advance (and you could get someone to help you) of all the questions you could possibly be asked and work out how you would answer them. You could even rehearse the interview with a friend, to make sure you won't be stumped by any tricky questions (though try to avoid sounding in the real interview as though you have memorised answers!).
Apart from that, bear two things in mind: interviewers make instant judgments so be charming with a nice smile as you walk in, try to avoid clammy hands or looking TOO nervous, and make sure you are dressed appropriately for the job. The other thing is this (and speaking as someone who has done a lot of hiring, I can vouch for the truth of this one): always remember that when you walk into that room, the person on the other sideof the desk REALLY WANTS YOU TO BE THE RIGHT PERSON FOR THE JOB. So it's up to you to do nothing to dissuade him/her that that is the case!