For Example, I go to vintage/costume balls, which happen to be ran by different groups.
At one, they post the whole playlist for the night, and since it's such a huge hall and hard to find anyone. Dancers will arrange their partners well in advance and have a general meeting area. Generally, it's accepted that if the song has gone a bit and the partners haven't found each other, they get a new partner to finish the dance. Problem is this makes it hard for new people to grab a dance with the experienced regulars.
At the other, playlists aren't posted, but it's a smaller hall so it's easier to find your partner quickly. Dancers, typically, will just promise the next waltz or polka, with someone they really want to dance with. But here, it's a little bit more frown upon if you monopolize a partner.
But most conversations go this way:
(Waltz playing)
A: Would you like to waltz?
B: Sorry, I'm unable because sitting this one out, but how about the next one?
A: That would be great, meet you by that post?
B: Terrif.
But if you promise a dance, remember that promise, because if you don't, you might have lost a future dance.
Hope this helps.
-TheDitz