Steve, I understand your question to be about group dancing, (not something like solo step dancing). Here are a few thoughts:

I play regularly for contra dancing and Irish ceili and step dancing, have a little experience with Scottish country dancing and Irish set dancing, and just a passing acquaintence with English country dancing....

Having a regular rhythm is more important than getting in every little note for those kinds of dancing. So newer players should simplify tunes rather than try to ornament them or play every little intricate passage. Playing at a regular, consistent tempo is equally important.   If the dance is "called" then the caller can always give cues to speed up or slow down the tempo if necessary. Listen to other players to hear what gives lift to the dancers. Accompaniment instruments should emphasize the downbeat, help give emphasis to moves like a balance and swing, etc.

Knowing what kind of tune is required for the dance is very helpful.    For contra dancing reels or jigs are usually all that apply, but for some dances a jig might work better than a reel, or vice versa. Ceili dancing usually specifies a jig or reel, and a few dances require a specific tune.

For Scottish dancing, the requirements are stricter, and often particular sets of tunes are needed, and the tunes are switched in a certain order (8 x 32 reel, for example, means play reels 8x through, but they are often played in a special sequence- four reels played 12342341 or three reels 12312321.   Sometimes the dance specifies a particular tune.

I'm sure there are more experienced musicians when it comes to English Country Dancing, but I think that the dances often go with a specific tune.

Tempos- for contra and ceili dancing are usually around 116-120 bpm, but it varies, and again, the caller is a good source of input if the music is too slow or too fast.

Learning how to put together medleys is another topic. For contra dancing, having a key change in the set often energizes dancers.   There are no hard and fast rules for medleys, but if there are instruments that need to move capos or retune, that affectst the medley. Matching tunes to their relative minors (G- Em, D-Bm etc) works well, as does changing in fifths- like moving from G to D to A adds energy too.   These rules probably work for ceili or set dancing as well.

Less experienced musicians benefit greatly from sitting in with experienced dance musicians. It is very helpful to have 1 or 2 core players to provide guidance and communicate with the caller or dance organizer, then offer leadership to select tunes, set tempos, etc.

Learn to watch the dancers. Some tunes don't work with some dances- the emphasis falls in the wrong place for the figures.

I might have more ideas but that's a start
Sharon