1. Acquire Molly, Acid, Ecstasy, or Coke (or all of the above)
2. Post up and look sketch
3. Look for extremely scantily clad ladies dressed like fucking rainbow bright
4. Ask them if they need anything?
5. ??????
6. Profit (aka get laid or get paid, or both)
Or you could just go in the middle of the crowd and play the odds dancing with/humping random chicks wearing next to nothing. If it"s a big enough show (300+) you"re bound to eventually find a decent looking chick looking to bang one out after the show. Unless you don"t like banging people on drugs, in which case I would recommend you not try and get laid at a techno show/rave.
I"ve got a buddy who was an Ambassador for Bassnectar (stupid job title, I know), and his job is pretty much to help out people in the crowd with water and such, as well as do whatever other miscellaneous bullshit that doesn"t involve stage tech, mostly selling t-shirts and cd"s. This guy has no job (ambassador gig doesn"t pay, you just get in shows for free) and honestly he"s not that great looking, but he pulls in an outrageous amount of ass at every single show. He pretty much is doing nothing else with his life other than going to free rave shows and banging rave chicks.
EDIT: Almost forgot, don"t show up to the show dressed up like you"re going to a date, wearing nice clothes, or generally anything else that makes you look mature (no collared shirts, no button-ups, no nice shoes). The older and more professional you look, the more people will think you"re an undercover cop and treat you like a leper. If you"re older (26+ or especially past 30), you"re going to stand out so dress extremely casual: tennis shoes, t-shirt, shorts/jeans w/e. Raves are one of the few places where you can dress like an immature faggot and it"s completely acceptable, and in fact, encouraged.