First impressions count. Project a professional image. In most cases, wear a suit to the interview.
Most companies are still fairly conservative.
Your main task is to choose clothing, etc., which will not take the interviewer's attention from you and your qualifications. Absolutely no gum, candy, or cigarettes. Dress for the job you want, not the job you have. Wear a dress watch. Arrive a bit early, go to the restroom, and check you appearance.