I have the same problem which makes finding a job very hard. Plus not having a piece of paper from a college saying you wasted a ton of money to get it, that makes it even harder.
I try to go over my resume and my application, I always keep a copy for myself and I bring it into the interview with me in case I need to reference it for some weird reason. One thing I do is to have a little snack and relax before the interview. I always arrive early for the interview as well so that I'm not tense from dealing with traffic on the way. I also go over some of the general interview questions in my head and how I will answer them. Go into the interview in a professional manner. Be polite use your manners, yes sir, no sir, etc. Dress appropriately for the interview. Some businesses require formal dress others are casual dress, and a few are actually normal attire, however still DO NOT go to an interview with dirty or torn up clothes. Go in like you are ready to run the company. If you know the company you are interviewing for, look them up on the internet and research them a little bit, some companies will actually throw in a question or 2 about what you know about that company so be prepared. Don't go in there with a cocky I know everything attitude either, that'll get your job outlook tossed out right then. Explain to them what you know and can do, but say you are always learning new ideas and concepts to make yourself more knowledgeable in the field.