The most important thing is to play a tune with clear phrasing and a steady beat at a danceable tempo. Without this there is little you can do to make up for it with awesomeness elsewhere: people won't know when to step, when to balance, or where they are in the dance. And if you confuse the caller, the caller will confuse the dancers even more. Dancing, if I have to start counting to keep track of where I am it becomes way less fun. Don't force the dancers to think.

Once you have something that provides the necessary cues to the dancers, you have a lot of freedom to add or change things. It's easy to get carried away here with all the possibilities, so the main thing to remember is that your attention span is much shorter than the dancers'. You are focusing fully on the music, but they are thinking about the people around them, perhaps a conversation, variations they might like to play with, where to go next. (This makes playing dance music very different from playing a concert: as the band you are not solely responsible for entertaining them.) If an interesting rhythm comes into your head, sure, go ahead and try it. Just don't switch to another one (and another one) without giving each several times through the tune. Your ideas need to grow on the dancers; they take a little while to get into them, and you don't want to yank them about too much.

Supporting the dance is primarily about indicating the 8-count phrases and the beginning of each time through the dance. (When we think of a 'good' tune for dancing, that's most of what we mean.) This is why you can pair just about any tune with just about any dance. When the match between the music and the dance is tighter, however, it's really nice. You do this both by choosing tunes to match and by altering how you play the tune. As a musician, a good way to get a better understanding of what sort of music supports different figures can be to accost a caller and ask them how they determine what sort of music to request.

One challenge in trying to maximize fun for the dancers is that sometimes the right thing to play is actually kind of boring for you. Perhaps you're the bass player and the tune is in D: it can be really powerful to play 'D' on each down beat all the way through a tune, 64 times in a row. Really dull. Or perhaps you're playing dancing bear on fiddle while your bandmates play all sorts of outrageous chord substitutions. The tune is so simple it's hard to keep going, but the contrast between the repetition of the melody and the variation of the chords can work really well.

This is part of accepting that you are a member of a band and that the goal is for the whole band to sound good. I used to try and play the mandolin so that the mandolin sounded good. More recently I've realized that in a band with a piano and fiddle the most important thing I'm adding is percussion. The piano is a great rhythm instrument, primarily because of it's excellent range. I'd rather dance to a fiddle-piano duo than a fiddle-guitar duo: without any notes below 83hz the guitar is missing something. What the guitar has that the piano lacks, however, is the option to put some percussive grit in. The fiddle can do this, but they're usually busy, so I take this on with mandolin. I also think about this when micing the mandolin: considered on its own my mic placement is tinny, gets lots of pick and fret noise, and doesn't have the full rich tone possible with some other placements. But that's not the right environment to evaluate it in because that's not how people will be hearing it.

I know some musicians who disdain 'cheap tricks': simple things the band can do that make dancers shout. If, when the energy in the hall is right, you play a V chord (E in the key of A) over the whole B2, or even bIII-IV-V (C-C-D-E in the key of A), it's totally unsophisticated and not completely harmonious, but the dancers sure love it (video, see 7:00). Similarly, you can leave a beat of silence right before a balance, especially at the top of the tune (video, see 5:30). I think part of why musicians don't like these is that they're almost completely disconnected with the melody. You can pound on the V in any major tune and get the same feeling when you go back to the I. But the dancers like them, so I'm all for it.

Trying to make the dancers have the best time you can means trading off some of what you would do if you were playing for yourself, but having this kind of external evaluation metric (how much fun are the dancers having?) is actually something I really enjoy about playing in a dance band. It's really satisfying playing to a happy crowd having a good time and enjoying, among other things, your music.