I usually play conversational "red rover." What that means is that I'll be relaxing, talking to friends that I showed up with, or dancing. If I hear a hot girl talking about something I know a lot about, I'll usually chime in with a joke or an opinion contradictory to hers in order to create the impulse in her to respond to me and defend her position.
I also don't just focus on one girl. I work an entire room if I can. I make friends with the guys in the area first. When the guys like you, you have "social proof" that makes you "safe" in girls' eyes. Barrier one broken down. If the guys who are supposed to defend them from creeps and stuff let their guard down, you can't be that bad, right?
Winning over her girlfriends is next. Chatting them up, finding common ground. For the uglier ones I don't want them to catch onto what my real goal is, so I try to keep it business and career related and find some common ground and good reason to maintain contact. Usually a referral to a friend's business/service or something. In any case you build a friendship and keep it platonic.
Then comes her. I tease playfully. I put my arm on her lower back or upper arm if her body language looks receptive. I smile, but not in a cheesy way, more like I'm up to something no good, or that I know something that she doesn't and it's hilarious. I laugh softly and with a little bit of cockiness. Not so much to make her think that I'm better than her, just enough to get her to think, "Oh WOW! This cocky guy likes me! I must be something special!" Now she feels safe and special because of you.
I also like to, if I'm really feeling it, order a unique, almost unheard of cocktail for her. I tell her something along the lines of, "You have to try this drink that someone made for me while I was traveling in [insert interesting place here]. Nobody knows about it, but it's amazing." (On a side note, a spending limit for others on a night out is $40.) This shows that I'm well-traveled, a person that likes to try new and interesting things, and that there's probably a lot more to me that she hasn't seen yet: a life that she might want to be a part of and that she'd better make a case for herself to stick around if she wants to see more of it. This makes her happy.
At this point, you've reached the holy trinity of what women want: To feel safe, to feel special, and to feel happy. They overlap, but that's the goal IMHO.
After that, you just gotta pull the trigger. Well, this is what works for me.