I was nervous on my first two interviews, though I landed both jobs. I stopped being nervous after I actually had a couple opportunities of being the interviewer. Then I began witnessing first hand how people royally screw up interviews.
Be 5 minutes early, never late.
Be prepared, bring your resume & letters of recommendation from non-relatives.
With your resume, have a professional looking email address, if possible keep the resume down to one page [on average, an interviewer spends less than 30secs reading a resume]. Give your phone number, but make sure your voicemail message isn't unprofessional sounding. Make sure there are no grammar or spelling mistakes, and that the resume is properly formatted. Buy some resume paper even. A cover page will do you well too.
Dress appropriately for the interview, and even if you go to a business just to pick up an application, make sure you are dressed as if you were going for the interview [because they might give you one on the spot].
Answer according to what you were asked, and don't babble. Speaking of answering-- before going on the interview, think of questions that you may be asked and think of the answers you will reply with. If you're going for a childcare job and the interviewers asks you what type of activities you would do if you were given a group of children, don't respond with "Oh, I love movies and cartoons, so I'll have them watch movies and cartoons!"...she was not hired. Don't give stupid answers like that.
You're probably going to be asked to give an example of a situation during your work where you were faced with a problem and how did you absolve it. Think of a good example before the interview.
You're also probably going to be asked what you think will be your responsibilities if you get the job. Another thing to think about thoroughly prior to the interview.
A thank you letter also is a great addition and you will stand out from the crowd of other hopefuls.
shadha-