Just say hey, introduce yourself, and ask the standard get to know you questions to establish a rapport.
"What year are you?"
"Where do you live?"
"Where are you from?"
"What classes are you taking?"
"What's your major?"
etc.
And then get her a drink, ask her to dance, play beer pong, or whatever is going on at the party. You can gauge her level of interest based on her answers and willingness to do those things. There's no magic moves or lines that I've found to work. It's like the other posters have said... It's college... You just have to show up, not be hideous, and show some interest in them. You just have to get lucky and find the right girl who is also looking to hook up. And if you're going to the right parties, that should be more than half of them.
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-Merc