I dont think costumes have anything to do with a good "rave". are you talking about massives, like Ultra, Wemf, Starscape to name a few? or a Jump off at a club, or an outlaw with no permits, or even a weekly?
a party as I call them need
A good SOUND SYSTEM..shitty sound forget it.
a good vibe, hard to find

good djs, they dont have to be famous, locals often play the same tracks as headliners but the music needs to be on point.
Friends, I love going out with my friends and meeting up with other friends fromt the scene
honestly i know this sounds terrible, but the best parties ive been to have at least one OD. Well not all but most....
Also it depends on what you want to get out of the party experience. I go for the music so to me sound is very important, followed by line up, followed by friends, then the venue, everything else is secondary
a bad venue can fuck a perfectly good party up.