Here are some suggestion:
1. Research the company. This should be easy with the internet. Use this informaiton in your interview. It will make you look well prepared and resourceful. Also helps with #2 below.
2. Ask questions at the interview. Have some prepared and also take quick notes of new questions if the interviewer is doing most of the talking. Be sure to have thought of why you want this job. Why this company. You will be asked. At the end of the interview ask them if they have any concerns about hiring you. This will allow you to address those concerns instead of leaving them as a great unknown when they make their final decision.
3. Accentuate what you have accomplished but do not brag. Be sure the inforation you are presenting is relevant. If you won best french fry cook at your first job as a teen do not bring that up if you are applying for an IT position obviously.
4. Smile. I recently had an interviewer tell (at the end of my interview) that she will not consider any applicant who does nto smile at least 3 times during the interview. (BTW . . . I was smiling

)
5. Arrive early, but not too early. I try to arrive approx. 15 minutes before the scheduled time.
6. Dress appropriately. If you are not sure over dress. You may want to go by the place (if possible) and see what the other staff are wearing to get an idea. At one interview years ago I went by and notice that the uniform was blue polos with Khaki pants. I wore a polo (dark grey) and Khakis. If you already look like you fit in and work there it can make a great impression. Personally I wear a suit to every interview. Of course I was interviewing for associate attorney positions.
7. Look the interviewer(s) in the eye.
8. Have copies of your resume and reference information ahndy. You may have already sent one in but undoubtedly you will be asked for another . . . this always happens to me.
9. (GOOD ONE FOR US CIGAR SMOKERS) Do not smoke a stogie before going to the interview. Some people may be turned off by the residual smell on your clothes, hair etc. I personally refrained from smoking all day before my recent 5pm interview.
10. Turn off the cell phone, beeper, PDA etc. AN ABSOLUTE MUST!
11. Be yourself. Do not try to impress the interviewer(s) by trying to be something that you are not. Do not suck up. Good managers do not want a suck up. Those that do you would not like to work for.
GOOD LUCK!!