wow. You guys that all read the bible and have never used any of that canned advice are damn cool huh?
I would suggest you take advice from the people that HAVE experience. "bla bla you have to build attraction, and get her interested, i'm full of bible bs"
Last year I went up to one of the most popular girls in my class (it's not that big of a deal cuz i go to a small school) but we have done nothing more that chat in class. She didn't have a date, prom was cumin up real soon, I said "hey (hername) you, me, prom?" obviously expecting the 'yeah' that i got along with her blushing and w/e.
Anyway, it's not that complex. If you want to know what to say I would suggest a few things. If you KNOW she is attracted to you, "hey you're going to prom with me, right?" that's a good/rare one, works great. If it's more of a friendly thing, hey who are you going to prom with? When she says no one/doesn't kno yet/w/e well why don't you show up with me/same here, let's go together.
You want something casual and confident, yet not like a middle age pervert type. Just be confident the words don't really matter all that much anyway.