I've said it many times but the ideal is getting to know the staff and the patrons, visiting multiples times to achieve this. When you're part of that crowd, you have carte blanche to do pretty much anything.
I was in a fraternity in college, and this is exactly the reason why fraternity brothers get so much play, because it's "your house", and you can simply approach anyone or do whatever you want, because it's either literally your house or (in the case that you're at a different venue) you have the social permission to act as such.
In one of my recent reports, I approached a girl sitting at the bar this way. Instead of approaching her directly, I ordered a drink from the owner (my friend), and I said like "who's this girl, huh?" then when she turned to me I introduced myself. From that kind of higher social position.
Barring this, you simply just have to approach whenever you feel like it. Being not-alone is a big thing here. If you're having fun with a friend or two, your "fun vibe" becomes a kind of bargaining token that you can exchange for conversation. If you and your group are having more fun than the group you're approaching, you are the ones with the upper hand, because you are "the party". Bonus points if one of the members of your party is a girl, especially a cute girl.
I feel that getting a higher social position in these venues is much easier in China because, as a foreigner, you're a unique special snowflake and people are much more likely to give you attention and status. Like at the bar I mentioned above, the sad reality is that I'm only friends with the owner and the frequent-goers because I'm a white foreigner. They thought I was a cool curiosity and wanted to add me to their gang because of that. This doesn't mean the friendship is fake, it just means that the introductory stage is cheesy.
