How do you approach?
The answer is: You don't.
Girls are the ones who initiate contact by sending indicators of interest. That's how it always is.
Yes, the guy is the one who does the 'approach', but he never does it out of the blue. A successful approach is always, I repeat, ALWAYS preceded by an indicator of interest from the girl.
A guy would never approach a girl out of the blue, because that would be creepy, obnoxious and harrassment. It's only an acceptable thing to do when the girl made the first step and gave you the signal that she's interested and that she's okay with you approaching her.
That is the difference between sexual harrassment and a romantic approach.
I came to that realization through many conversations with goodlooking and sexually successful guys. I asked them about girls and dating and it was always the same story. None of these guys were actually coldapproaching, or were randomly going up to girls they didn't know. Shit like that doesn't happen. All their success was based on girls giving them signals and they just picked up on it.