Alrighty, here's what I'm gonna suggest for you:
Top: The classic T-shirt. Here's the kicker: not too loose, perhaps with a design on the front. I leave the design up to you, but I was thinking something along the lines of Threadless tees:
http://www.threadless.com/ I would avoid wearing a really bright colour, as you might come off as a bit blinding on stage.
Bottoms: Again with a classic: jeans. You really can't go wrong. Again, make sure your pants aren't too loose. I'm not saying that you should wear super-tight pants if they aren't your thing, but make sure that they fit you well. For style, pretty much anything goes. If you like the distressed look, I say go for it. Any colour will do as well.
Shoes: I would go with a really classy-looking sneak, which means that I would recommend some type of Converse, preferably high-tops. They are pretty much the epitome of badass shoe. But if you don't have the money, any sort of basketball or skateboard shoe will do.
Extras: I wouldn't overstyle your hair too much. Just do whatever you normally do. If you get cold, wear a hoodie or cardigan. If you go with a graphic tee, make sure that whatever you wear over the top is a solid colour.
How's that?