If you're interested in dancing in blades, or even old skool rollerskates then you could try out the Roller Disco
near Kings Cross, either bring your own skates or hire them, although admission includes skate hire, so it might be easier to use theirs. It takes place every Thursday from 10pm - 12am and Friday 8pm- 2am, but only available for those over 18, due to the bar, proof of ID may be needed.
If you like someone's moves then go ahead and ask them if they'll teach you, especially if you notice that they're wearing a uniform. The staff'll be happy to help you figure out some new moves, so you can follow their lead, if you're new to the whole idea of dancing in skates, and feel a little intimidated by the more advanced dancers, then this is a great way to learn, and a little more exciting than skating in circles to the music.
So get skating!