It's called 'dance floor' for a reason; to dance! Dance/grind with the girl you want to, ask her name. Nothing more. You could tell her that she kinda sucks at dancing and you're not impressed. She will most likely will jump trough your hoops.
After 1 or 2 songs tell her you're going to the bar and drag her with you. You do this by physically take her hand and guide both of you to the bar/lounge to get yourself(!) a drink. You can also tell her you're going to get a drink and she should come with you. Girl will most likely will shit test you by asking if you would buy her a drink, and off course you will pass (by not buying a drink for her..)

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This also leads to this topic:
get-women-to-commit-to-interactions-wit ... 19874.html
Oh, and this is all theory. It pretty much depends on your body language and your confidence in general. If those sucks, you will not even get her to the bar with you for example.
Share your opinions!