And don't think just because you work there you don't have to dress well. I suggest a suit, though slacks and a tie will work well, too. Or if it's on the clock make sure you have an extra uniform that's been dry cleaned and pressed.
Be up on company policy, I'd suggest flipping through the policy manual and your protocols a couple times.
Yes, sir and no, sir, even if you are on a first name basis with the interviewer.
Relax, if they're giving you an interview, they think you'll be a decent fit for the job, you just have to show them why you're better than the other guy.