There are lots of ways to prepare for a job interview, but only a few that are a truly simple way to get a leg up on your competition. Try these on for size:
1) Bring lots of copies of your resume. It's frustrating when you walk into an interview, realize it's a panel of employees, and only have one resume to hand out. Pass out your resume to everyone who doesn't have one -- it will make you look more prepared and professional.
2) Bring a water bottle -- even if you don't use it, you'll be happy you're not ducking out of your interview because your throat gets dry or you start coughing.
3) Keep all of your materials in your left hand, all the time. This tip is easiest for left-handed people, but give it a try. It makes it easier for people to shake your hand without you having to shuffle things around or drop items. Any time you can smoothly transition is an opportunity to appear calm and collected.