If you are in public, smile and make eye contact at least twice before you approach. That way if she smiles back, you know she is interested and she's going to wonder if you'll approach her. Don't go immediately after she smiles back at you, but linger for a while, talk with your friends. It will peek her interest. Casually stroll over and say something relevant but don't compliment her just yet. Ask her a question. DO NOT SAY, "What's up?" "How are you?" or "Have you been here before?" Those are all a tad cheesy. Say something like "So what are you celebrating tonight?" Something that will get her talking. Then, ask her what she's drinking and if she would like another. If she obliges, most of the time she will feel obligated to talk to you for a bit longer. Maybe ask her where she's from, or something, but DO NOT stay with her the whole time. If she came there with her friends, she wants to be with her friends, period. Perhaps after a minute or two of conversation, say something like this, "Well, I've got to get back to my friends but it was nice talking to you, I think you're beautiful and would love to see you again sometime." If she says sure, get her phone number and then LEAVE HER ALONE. She will wonder where you are, who you are with, and what you're doing. She will look forward to hearing from you, because you have just made yourself mysterious and charming. Good luck!