Another tip... try to get yourself paired up with an experienced rusher. Lots of times chapters use a two-on-two system, and that way if you get tongue-tied, there's a more experienced woman to help you out.
This is a tip for all rushers, but especially useful for newbies. Come up with a specific answer to this question:
What made you choose XYZ? Why did it stand out above all the rest?
Got an answer in your head? Great! Now write it down. That's important.
Also, have 3 or 4 go-to questions to use in case conversation drags: "What's your favorite movie?" is always one I like. The ideal question will have nothing to do with sororities and give the PNM a chance to relax and talk about herself in an area where she feels comfortable. "Do you have any pets?" is also another good one. The great thing about these questions is that after you and the PNM have chatted about her favorite movie or her German Shepherd, you can then turn the conversation gently to your chapter: "Yeah, I'll never forget the time when my goldfish died and my sisters held a funeral..." That sort of thing (though maybe not quite as morbid).