Being in charge of a monthly "open band open mic dance," I rarely prepare -- but I usually have at least a couple of dances in mind, just in case.  I never know if another caller will show up or if a room full of newcomers will show up.  It's a small venue and the regular dancers are forgiving.

For a regular dance, I do like to have a program and start with at least a sketch of a plan a week in advance.  If it's a band I haven't worked with, ,I try to have a plan to them at least a week ahead of the dance.  For our regular musicians, all they want to know is where the Balances are, are there any Do-Si-Dos (usually a jig), Down the Hall & Back or Hey, and whether I'm using a Chestnut with its own tune.