I think, overall, there are a few rules to follow here:
1) Keep yourself groomed and clean. I usually shower right before I head out to a gig if at all possible.
2) Dress to Impress. If not to impress, then to be a part of the crowd of whatever style you're going for or type of girl (or guy) you're into.
3) Be confident. If you're timid and shy, there is a very good chance people wont care who you are. Make them care enough to notice how confident you are, but don't be a hatefull jerkface.
4) Have fun. If you look like you're not having fun, people wont want to be around you. It doesn't mean that you have to dance (definitely not a selling point for me), but it should mean that you're having some conversation and/or making small talk with some people who watched you.
Shmoozing is a big part of the before and after show deal. People will be more likely to come back and watch you if they actually enjoyed being around you.