show up early and use their facilities before the interview to wash your hands and check yourself out in the mirror. You don't want clamy hands or boogers. Research more then just the company, but if you know the name of the person who will be interviewing you, find out what you can about them from professional connection sites. Remember that you are there to display your best qualities, not only your smarts but your personality as well.
Invest the money in getting your resume professionally printed if you can't print it yourself on a laser printer... and purchase a few covers for it. I got some for my interview at Kinkos for like 50 cents each.
Relax, be yourself and on last thing. You are interviewing them just as much as they are interviewing you. prepare a list of questions so at the end if they ask you if you have any, you can glance over the list (serves two purposes... first your questions get answered, second, if they cover everything before you can ask, it shows that you thought things out and that looks good)
Good luck! Also, I did an internet search the day or two before my interview for "interview tips" that's where I got a lot of the stuff above... it's pretty generic but I got the job I was trying to get, so hopefully it will help!