I have to say, dance floor game is tricky, but the key is to look like you are having fun. Girls LOVEEEEE guys that are having fun.
For instance, (and it all depends on the atmosphere of the bar), I was with a bunch of buddies that I knew from college. We met up one night a few months back and headed to the college bars (at the same college we all graduated from). We got pretty tanked and were on the dance floor. The music was decent (mainstream kind of music). What we did was, we have two guys pretending to "double dutch" (when two people hold two jump ropes and spin them around). the third guy is outside the invisible jump ropes and hops in and pretends to do a double dutch. Then eventually a bunch of people join in. We had the ENTIRE bar jumping in. It automatically dhv all of us, and it was just an awesome time. Girls kept coming up to me and saying we were so much fun, etc.
As posted above, another good thing is singing along the words and dancing along. If a girl makes eye contact, sing along with her, and get in on that. Its so silly and simple, but it works for me.
Another thing I do is, as we all know, when a song with a "dance" comes on, I make it a thing to know the dance. Eventually, I look around the room , see which girl is doing the dance, and then I go over to her and dance off with her. Eventually this leads to her dancing with me later on that night.
I've had NUMEROUS girls just dance with me because I was just enjoying myself. Thats what girls like, fun. So they see it in a group of guys and join in. It may be tricky for a girl to join in on a break dance of course, but it can help DHV.
Oh, another good fun thing to do as a joke (and again, depends on the atmosphere of the place), is have one of your buddies take off his belt (or you), and use it as a limbo stick, Girls will get LOW on that. But the timing and mood in the bar has to be right. We always drag girls in on it and they are more than willing to join, just needed a little persuasion.