First off, if you are interested in shooting women, you have to understand them. Girls love attention. And especially when they are with other girls. Also, once an idea is in a woman's head, it stays there for weeks. What I am saying is, when you see a girl you might want to shoot, approach her and explain what you want to do.
Now having said all that, girls also have a thing they call "the creep factor". If they sense that with you, you're out of luck. It's all in your approach. You have to have confidence in what you are doing. What I do is approach with a smile. I say, Have you ever done any modeling? Whatever her answer is, then I say, I am a freelance photographer, and I noticed you because I think you have a unique look. I would love to shoot you sometime. Tell her, It's a win-win for you because you get free professionally processed pictures just for volunteering your time. You can build your portfolio, or send them to family or friends or facebook. I am NOT interested in nudes or semi-nudes, just some shots that will accentuate your look. Tell her to bring along a friend, or a family member. This gives them a little piece of mind that you arent some weirdo. Give them a business card(have some made that are professionally done, dont create one on your ink jet printer, people will notice that right off and it makes them think that you are cheap and unprofessional.)
Even if she doesnt commit right then, she will think about it for a while and chances are will contact you. Usually when you are talking to her, especially if she is with her boyfriend or husband, talk to both ot them. Let them know that this is purely professional and you are always looking for pretty and unique girls to broaden your own port. I think what also helps me is, my wife is usually always with me. She tags along on the approach, and it just backs up that I am not a creep looking for some racy photos. Plus my wife is my assistant and her name is also on the business card. Again, reenforcing that I am not a weirdo.
LIke I said, most attractive girls absolutely love to be the center of attention. And after they show the pics to their friends...your phone will get very busy. That's how I do it and have had great success. Just dont be shy.