A2A, I’m not very good at this at all. I can say that there’s no one-size-fits-all solution here.
I can tell you what not to do. If she’s alone, do not ask her why she’s alone. Do not try to teach her how to dance. Do not just say hi with no conversation topics planned. Do not compliment her more than once, pick that compliment out very carefully. Do not “neg” her.
If you can’t figure out how to have a conversation with a lady you just met at a bar, don’t approach her. You need to think “2 moves ahead.” So if you’re thinking about going up to her, you need to know what you’re going to say to her after ‘hi’, and then you need to know what you’re trying to accomplish assuming the conversation goes well. Phone number? Invite her to another bar that you want to check out? Back to your place? Understand what your intentions are and you’re already doing 10 times better than most of the other yahoos.