How do you tell if a girl wants to dance ans how do you know she is actually interested?

Often times I'm out with a group of friends at a bar or club dancing. We usually go out with a few girls, mostly friends because it makes it easy to approach other women around us when we are all having fun.

The problem is it's hard to tell which girls around me are interested. Even the ones that seem to be dont always work out.

I've been given the eye by girls and that's usually pretty clear but other times girls will dance directly next to me or in front and lightly bump into/against me occasionally (seeming deliberate) and that will be about a 40/60 chance of them trying to be sly and dance with me or they are just not paying attention and are caught a little off guard when I approach. Another problem Ive noticed is that sometimes it's only playful, as in I'll see a girl and we will dance for a bit but once I try to get closer/make a move I'll get shutdown which is fine but its gotten hard to tell when it's just having fun or are attracted to you.

Do you guys have any tips or advice for those who have decent game on the dance floor but cant seem to get to the next level?