pyraxis, have you got a Little Black Dress? that'd do fine - they always do. then you can have great fun with jewellery.
if you're dark with pale skin, don't go for too light/neutral a shade of lipstick, cos you'll just look washed out. don't go for a makeover - if you're allergic to anything, you're fucked, and no time to remedy it, AND you'd have to keep it on for hours, and they'd have to apply it with a trowel if it was going to last.
make sure you feel comfortable - i.e. that what you're wearing is an expression of YOU. i rarely fit in with what i'm "supposed" to wear, but then i have a reputation of being completely eccentric and outlandish in my attire (think viv westwood, gaultier, zandra rhodes in the 70s), and so get away with it. as long as you stay within the bounds of decency, get in there and slay 'em - if you do it with conviction, people will assume it's all intentional, and that you're supremely confident about your own "Look". people expect me to try and get away with murder, so i do. (they think it's complete confidence on my part - little do they know...).
incidentally - comfortable doesn't necessary mean flat shoes (sorry, shima) - for me, comfortable sometimes means wearing four inch platforms/heels, cos that's who i feel like being - psychological, as well as physical comfort is important, for me.
as for the behaviour bit - flick your hair around all evening, and you'll a) look like an idiot, and b) annoy the fuck out of anyone near enough to get caught by bits of flying hair. flicking your hair is massive flirting (i play with mine all the time, and so get caught out on that one, when i don't mean to). choose who you want to be, and then do it - you do role play, don't you? it's like that, and the fun thing is to maintain it, all evening.