The single MOST IMPORTANT thing is that you make eye contact before approaching. The eye contact he gives back should show some degree of interest. Without that pre-approach eye contact, it never goes anywhere, even if it could have otherwise. For example, a cute girl tried to talk to me last night as I was trying to get a drink at a crowded bar… she came out of nowhere, my mind was elsewhere and I was slightly annoyed by the unexpected approach so I didn't get into any conversation with her.

The man needs to see you and assess you first to get into “mating dance mode”, and this only takes a nanosecond. By making eye contact, you give him that opportunity and create some nice tension. THEN when you approach him you are releasing the tension (building and releasing tension are crucial rules of attraction). After that you only need to bait him to continue the interaction by being interesting, then transitioning to the point where he's leading, or it's at least 50/50.