[quote=Dervish]Also, dress presentably. This should be painfully obvious, but the amount of idiots go go into job interviews in their street clothes is staggering. Look like you give a shit and want to convey a professional image. Clean yourself up, put on a nicely ironed dress shirt and paints, a nice pair of shoes, and act like you have a lot to offer.[/quote]

This is perhaps the most common piece of advice I ever see people give.
And to add to it I say it varies on the culture of the place you're applying.

You have those really stuck up places who will turn you down just cause you weren't wearing a suit when you dropped off the resume in a mailbox (Not even say for the Interview itself). Then you have those people who may think you're trying too hard if you show up all dressed up to something like McDonald's.

Try not to push too hard in either direction.
Don't go too, pressed, ironed expensive suit so you don't throw people off or give the impression that you can't handle any dirty work (or that you're that desperate for the Job).
But do try to look professional and nice at least so people can take you seriously.