Also a good tip is to meet as many girls in the house as possible.  And really show how enthusiastic you are about joining.  Also, appearance is a factor.  Not that they are going to decline you if you are ugly... we aren't that shallow.  But a girl you dresses to impress while rushing is going to look a lot better than a girl who just came from the gym in her sweats.

I suggest doing some research on the chapters you are most interested in and definitely target your favorites.  Find a sorority that has ideals you agree with, a philanthropy you support, maybe even a sorority that has a symbol that means something to you.  For example, one of my sisters chose our chapter because our chapter jewel is her birthstone, and that was meaningful to her.  And express that reason to the girls you talk to and they will be impressed in your thoroughness.  A lot of this information can be found on chapter websites.  If you don't express interest in a certain chapter, the girls are going to think you are more interested in going somewhere else.

Basically sororities are looking for strong women who will represent their sorority in a positive light who will be great active members of their chapter while fitting in with the ideals of their chapter.

Good luck, and I hope you find the perfect fit!