The modern trend seems to be 'play a tune until you're fed up, then switch to another', which I don't think helps the dancers much.

We always agree in advance with the caller how many bars we need for the dance (48, etc.) and how many times through, then choose appropriate tunes (typically three, depending on the planned length of the dance) to make the length right (in terms of number of bars). Playing 3 tunes is certainly more interesting for us in the band, and I find the dancers seem to prefer it. I've not noticed any dancers seem confused just because we've changed to a different tune, but maybe they do?

In spite of that, we do sometimes have to make decisions on the fly, and usually play a few extra bars or whatever is necessary. Our callers (we use more than one, not at the same time though!) seem good at communicating what's needed and we follow him or her.

Regarding organising the dancers, a couple of the callers we've played with use a wireless mic headset, and that seems a good idea - they can get amongst the dancers on the dance floor and physically sort 'em out if need be!