hey
how are you going? wow, you are so beautiful
what's your name?
*said genuinely, maybe mention a particular part of her that's nice (hair, shirt, etc), relaxed, confident calm, with a smile
It blows my mind how much guys overthink this...
It's one of the simplest openers, but it MUST be genuine, and smooth, with confidence.
If you don't know what to say next, just keep complimenting her. Sometimes I ham it up if she's an 8/9 and tell her she's got great style/she should model/why doesn't she have a boyfriend/she's the hottest girl in the club etc.etc.
Of course, it's gotta be from a genuine place, and you shouldn't be putting her on a pedestal, acting like a perceived pervert or being weird. You're just appreciating the beauty in the world and smiling as you express it.
Girls love attention. They love to be told they're special. Don't pretend to be anything. Just appreciate her. And if you're really being straight up and unapologetic about how she blows your mind, she will want to stick around.