I don't flirt, per se, I just go talk to the lady if she seems receptive....and you can see that in her eyes. It's really obvious. Dilated pupils, I guess; a little twinkle and a slight but perceptible smile.
I just go say "Hi, how are you?" and if she gives a friendly answers, I say "I'm Frank" and offer a handshake. Then I ask if she's new to the neighborhood or the club...depends where we are, but it's a fresher version of the ol' "Do you come here often?" line.
Then we simply have a conversation. That's when I learn if she's conceited, intelligent, interesting, has a sense of humor, and, of course, game.