edX
mac shaman
how about "hi, what did you think of class today?" or yesterday, or in general. start with something you know you have in common. if a gir's interested, "hi" is enough sometimes. if she needs to become aware that sh'e interested then you've to give her some reasons why. the more you talk, and the less you worry about what you're 'supposed' to talk about, the more natural it will all be.