You have to realize that a guy obviously alone on a dance floor like has been said previously has very low social value. This says to people either you are a loner or someone that nobody wants to hang out with. Either way you aren't exactly attractive. Plus if you are out there asking all these girls to dance the women on the floor have seen you get shot down by the first dozen and are already laughing at you being that guy asking every girl to dance. And if you are going to the same place every time by now you've already been labelled by any of the regulars.
If you had killer dance moves, my advice would be get out there to a good song, kick it up, get some attention and then walk to the bar where you can actually have a conversation with people. But you really need to work on speaking to girls and having real conversations with them first. There are lots of easy ways to start a conversation. Ask open ended questions they can't answer with a yes or no, make sure you are interested in them and not talking about yourself, talk about what interests them, etc. Start easy - quick hits like "hey, that's an interesting bracelet." or "wow this band is really good." You don't have to have a 20 minute dialogue. But you do have to do something.
Last night I was out on the dance floor with one male friend and three female ones. It was like child's play to strike up a conversation with one of the girls dancing around us. You get the eye contact, give them a smile and they smile back and you go.