You... talk to them? i was getting some cilantro at the supermarket and a fairly attractive girl near me was picking out cucumbers and i said slyly "Oh you don't want that one, it's a little too big for you". She looked at it smiled and said "Well, I think I can handle it". She asked me what i had in my hand, we started talking about cooking for a good ten minutes and then went our separate ways. i wasn't trying to pick her up or anything, i just felt like saying something. If you just talk to more women casually, it makes it easier to do when you intend to hook up.
Look at it this way, if you hear a guy talking about a rare game or anime or whatever, would you just go on about your business, or would you try to get into the conversation. What i'm saying is that if you see someone interesting (and obviously this doesn't always mean sexually), talk to them. If it something good comes out of it t then great, if not then you'll probably never see them again, and if you do, one of you probably won't recognize the other.