I'll tell you what I do
I don't usually go up to a chick unless shes already inspecting me. No point getting rejected by some fat whore.
If I see her looking for more than 3 seconds I just walk up to her and tell her that she looks good, first thing I say. Then I wait for her response it can get awkward after 2/3 seconds but that usually means she doesn't like your looks, if a girl thinks your hot she'll say it back instantly.
If she says it back I just ask a simple question based on whats around there, after that her name and her snap.
It takes guts to actually do it consistently tho, getting rejected can be brutal asf but thats why I don't go up to them for no reason