Bad ideas for first time ravers:

1.Wearing all that fancy expensive clothes on a party.Not just because everyone will know it's your first rave party nor because you'll be judged(ravers don't like mainstream but they don't judge anyone),but because you'll feel uncomfortable after few hours of dancing. You should wear most comfortable footwear you own(even Nikes),that rule stands for jeans too. If you want to be noticed,don't be shy wearing that weird neon top. That's what rave girls usually wear on this kind of events. For guys: you have a privilege to wear whatever you want,even though baggy clothes is preferred.But be sure not to mix it with that "gangsta" style lots of guys like to imitate these days. A party isn't a place where you will manage to "pimp" any "hoes" or whatever you guys call it.
Avoid jumping if you're not on a jumpstyle or happy hardcore event(WTF?). You can dance like an idiot,you can afford yourself to make those dance moves you're always been ashamed of,but PLEASE DON'T JUMP. Because jumping like a moron equals accidentally pushing or even lightly hurting people around you,and as you know,there are lots of people on ecstasy on raves.You have NO IDEA how badly you affect on people on any kind of drugs when you do such things.
3.If you are drug-curious,avoid drinking alcohol before trying them.That can be fatal,or at least disgusting,and I'm sure you don't want to spend your first rave vomiting and pushing your head in the toilet.....
....However,that can happen if you get bad (DXM,MDA,whatever) ecstasy pills,which is a common case even with old ravers. Try to inform about different pill logos and colors on the Internet,and also check the effects of drugs you plan to consume,they can suprise and shock people.In a bad way.
5.Don't be a rude jerk/bitch.
No matter how drugged that guy next to you is,if you have your glass of water,give him some. Or at least,give him a smile. That sometimes means a lot,and it's the best and simplest way to show you respect raver's only request - PLUR.
6.Don't try to seduce that cute girl with your "phrases that always work". She probably won't even hear you. It's not that meeting new people is something weird on these events,it's just DANCE. Dance is the primary way of communication on rave parties.
7.If you don't like that "annoying repetitive music" just leave. Don't force yourself to stay on a rave only because your friends or something. You won't have fun. Others won't have fun with you because you'll probably whine and just stand all the time. That's an obvious sign you should search for fun somewhere else,which isn't anything bad. Everyone has his own way of having a good time! PLUR