This was one of my problems BIG time. I would keep teasing and entertaining, but I would get nowhere. All you have to do, after you got her interested and kept her through the intial stage, is ask more personal questions. Simple.
This is where the conversation skills come in. Ask her name, where she is from, what is she doing, what did she do this weekend. It is important to get her involved in the conversation. If she willingly gets involved, then you know she is interested and can pursue something else.
For example, you just met a chick at subway and teased her about her choice of sandwich, how can she put mustard on a sandwich, doesn't she know that it is only for hotdogs?
Intro yourself exchange names.
Where is she from?
Her: blah, blah, blah (she is now contributing to the conv, she didn't have to tell you)
You: I hear that it is (blah blah) there, where I'm from it is (blah blah)
[this gives her two threads to talk about, what it is like where she is from, or asks where you are from, If she continues the conv. from this point, you are in.]
You/Her: Continue conversation
You can now sit and eat with her, or you can get her number and leave.
The more interesting and longer conversation you had with her results in a better chance of her not flaking at a later time.