Most Helpful Guy
Really depends on the geographic location of this "club"..
In smaller "hick towns" like the area I live in (low population) then your best bet is just a nice pair of jeans, some cute shoes, and a tshirt.. The real emphasis would be on external things like your hygene (hair, acne, etc - all play a role), and that's what would set you apart in this type of venue.
In more populated areas, you've got so many different "styles" of venues that I really couldn't give you "one correct answer".. You have venues for "mosh pits", "dubstep concerts", "hip hop clubs", etc.. So your gonna have to trust your gut or talk to some friends which frequent THAT specific venue frequently.
What I CAN tell you, is that it's not so much about your appearance that drags attention (unless you have a rockin' body, which I don't :P).. But instead, it's more-so how you behave.. If your having fun with all the people around you (yet rarely touching / dancing / etc with guys around you) then it makes you look a lot more appealing because your the fun girl which no one can tell if she's taken or not.. And that "natural curiosity" will spark a lot of interest.. Obviously it doesn't play out the same way if you just stand in a corner hoping people will come to you.. Be active and have a fun time. That's really the best way to go.