OK, I'm from the other USC, so the way we do things may be different, but here are the basics...
First round, wear something dressy-casual. It's the girls' first impression of you, so keep that in mind. Second round, something a little more dressy, but still sort of casual, third round dressy, and fourth round, formal. Your first day will be aquaintances with the rho chi, anyway, so she'll tell you if this is different. The rho chi is basically your "mom" for the week. She'll comfort you if you don't get invited back to a sorority you wanted. She'll congratulate you if you do. At my USC, she also carries around all of our stuff (lipstick, make-up, brushes, gum, etc...) in a huge bag so we don't carry in purses. As far as the getting cut for how you dress thing... sometimes this is true. Sororities look at how you present yourself, because eventually you'll be representing their sorority. If you get cut from a sorority that doesn't like the way you dress, then you weren't meant to be in that sorority, anyway. The thing is, and my rho chi told us this a LOT of times, you will go where you're meant to be. It hurts at first to be cut. Especially if you really think you hit it off with the girls (that happened with me... I was even told by the girl, "I want to introduce you to some more sisters, but we'll have plenty of time for that, later"). Eventually, though, you'll end up where you belong. GOOD LUCK!!!!!
