I really think it's funny how the first one to actually answer the original question as intended by the TS is the guy with the troll face avatar.
Basically what he said, I look for girls that look like they're having fun. If I someone chatches my eye I will usually try to make eye contact and smile at them first, if they a) are too drugged to even notice or b) scowl or turn away I won't pay them any more notice. Then again when I go to the club I usually go for the music first, hanging out with my friends secons and then maybe picking up a girl if the opportunity presents itself.
What you actually look like isn't all that important as long as you're not overweight, darkness, strobe lights, ecstasy (the feeling not the drug, although I guess the drug would work as well ) and alcohol (probably won't apply to your situation for a while as you're 15 and life in the US) will make just about anybody fairly attractive, slutty clothes are actually rather off puting to most guys I know. If you're absolutely desperate for the attention, dance dirty with your female friends, that usually does the trick. You should probably also avoid heavy make up, as it tends to run after a few hours of dancing.
And now I'd like to invite all female members to hit me with the moral hammer (does that expression exist in english? probabky not) for telling a fiveteen year old girl to dance dirty with her female friends ...