Preparation for Musical Tryouts?

I have musical tryouts next week before Thanksgiving break. We're doing Guys and Dolls. I always get so nervous and I'm afraid I'm going to do badly even though I can sing wonderfully the rest of the time. I also have to memorize and say lines. I'm trying out for Sarah's part for those of you who have seen it...any suggestions for me? I really need help and this is kind of last minute!! Thanks =]