The fact that you think all sorority girls are stupid, shows your sexism and ignorance. You have to maintain a certain GPA to even be able to stay in a sorority (in Canada, anyways). I plan on joining a sorority when I go back to school, and I am by no means, dumb or stupid. You use the word girls over women to prove a point, yet all you're proving is that you're still a boy, not a man.
OP I would definitely take some of the advice given above. Keep conversations light, simple and FUN. Making a girl laugh is more important than most men realize. Playing games invites a little friendly competition, which in turn can show off your confidence. Be open about certain things, but keep some mystery to you as well. Girls/women love mystery.
May the wind always be at your back and the sun upon your face. And may the winds of destiny carry you aloft to dance with the stars