This is difficult stuff "the dance floor is a trap" basically you can't "open" them because they're dancing they're already busy being entertained. The best thing to do is probably caveman it. Don't be try hard just go around dance like you're on a night and the roxbury and have fun. One technique that's great for dance floors is inventing a dance for your friends. Something just silly. Plan it and then all of you do it on the dance floor people watch and instantly want to be involved it's a great way to demonstrate leadership and playfulness. Me and my friends used to have a planned dance it was great people just come up and ask to learn. Let me know how this works out for ya:
http://puame.ca that's my own website pretty soon I won't being using this site anymore.