1. Hawkeye (about the talking, not about the self-deprecation) is right but you don't need to work that hard, even the shy ones will usually talk one-on-one. Ask "how was your day?" or "What's going on?" and then they will talk and talk and talk. If you don't want to poke your eyeballs out after a few minutes, that means you like her.
2. Many nerds get this far but then screw it up again by talking about their problems or concerns with life. Early in a friendship with a woman, if you do this you will be her friend, forever. You don't want to be her friend. You either want to be her boyfriend or you want to bang her. Listen, joke or positive story, listen. Then listen some more.
3. She will mention something relationship related (an ex, a former celebrity crush, what she likes men to wear)... Use this as a cue to talk about something SLIGHTLY sexual, you need to be savvy here. Your not telling her outright that she's sexy or that you want her, but you are showing her three things. That she made you think about sex "subconsciously", that now she has the image in her head, and you are comfortable enough to talk about SLIGHTLY risque subjects with her.
She will be the one who pushes it further. They always do. She will give you clear signs, if she doesn't then she is too unsure of herself or not a good communicator and you don't want to be with her anyway. Trust me.
(Note: by SLIGHTLY, I mean slightly. You have to be the judge but do not suddenly start talking about anal if she's talking underwear and do not talk underwear if she's talking about candle light.)
Women say looks matter, but they don't. They like to talk.
My personal limits, for when I was more single then I am now.
15-18 = 2 week limit
19-25 = 2 day limit
26+ = 2 hour limit.
These are/were my time allotments that I would wait for a sign, don't waste your time past this or you are the pathetic guy that they all make fun to the guy they're fucking because you hang around them all the time and listen to all their problems. Past this and you are their bitch. Of course, you may want to just be friends...