First time dance, and not alot of choices! Help!?

I have not many clothes that are appropritate for this dance (cold or hot outside and in gym wise) and i have a crush that is going to be there. Im kinda hoping to impress his and i need general ideas. He has a gf but he likes me a my bff he is being secretive about which one he likes more but i think it is me, so i really need to look nice! This is life or death, people! Lol. But i need hair, make-up, clothes, acceseries and flirtation advice from you. Guys and girls both welcome to answer thx!