I often see guys on a dance floor trying to start their pick up there. IMO, far smaller chances than approaching girl outside the dance floor (then You can take her to dance a bit if You wanted to).
The biggest mistake I see is that guys are just "dancing", more like pretending and trying to show that they can just move but their energy level is wayyyyy too low and they don't get attention they also never smile. Now think about it... if the guy like this walks up to a girl on a dance floor she doesn't feel like she's gonna have fun dancing with him.
Also to approach HB 8-10 You'd need bit social proof I guess (maybe some other girls dancing with You or friends greeting You while You're dancing).
What I do when I enter dance floor all by myself is just party like I'm having the best time ever

I smile all the time, I got high energy (I love dancing overall and I'm not afraid to shake my body, on occasions I got girls grabbing my ass even) and when I spot some girl giving me EC I look back and see if she holds it for few more seconds. If yes, then I can just start dancing nearby and try to focus my rhythm with hers and try dancing side-by-side and if she goes along with it and is with a friend I try to make her friend have a good time to so I dance back and forth side-by-side with both for example. Two-sets on a dance floor are rather impossible to split unless You got a wing or her friend takes a hint and leaves

. But it really doesn't matter to me 'cause I'm just there having fun. There are some really hot girls there dancing in pairs and you can see that when they dance really close to each other (You know, when You wonder for a second
Are they lesbians? 
) then most likely if You try to approach them they'll refuse.
To make this shorter, when I'm on a dance floor I'm partying like I couldn't have more fun, smile a lot and don't be shy to shake your body (don't forget the ass, girls LOVE it

). The fact that You're having the good time and You're not seeking some girl to dance with will result in some IOIs, like EC, or they rub against Your body and smile when you look at them. And proceed from there
Actually I wrote some FR about my night out yesterday and there are some bits about dance floor there

.
I'm not some mPUA but my friends tell me often that I'm a good dancer and I attract girls on a dance floor

.
Regards,
Mav-