Dress attire: Obviously wear a suit. Don't wear anything with red in it. Red symbolizes "hazard" and "caution". (The idea of the blue shirt/red tie is complete crap). Wear a light blue shirt - blue signifies loyalty and trust. Color psychology is very important in the interview process. Ties are also important - a tie with a simple symmetrical pattern signifies that you are organized and efficient. This is coming out of an interview book I read when I took a career class.
Grooming: Make sure you get a haircut a week before the interview so that any potential haircut disasters can even out during that time. Shave too... take off the goatee, sideburns, and mustache
Cologne: Do not wear cologne or any other fragrance that smells.
Sometime during the interview process, find an opportunity to bring up your hobbies and extra curricular activities. This will often lead into you telling a very interesting story about your hobbies that will intrigue the interviewer. You'll be surprised with how much this conversation will calm your nerves and even lead the interviewer to "seal the deal" in hiring you.
Last, treat it as a casual conversation with an author who wants to do a biography on you... you don't need to put on a professional facade as it can make your more tense and nervous. Be yourself - they are trying to evaluate your personality and how you interact with new people - so being yourself and being relaxed should make you appear more favorable in this respect.