Three groups of music always in work:

A list: Surefire set openers and closers that really COOK no matter how bad the travel was, the day was, the sound system is, etc.
B list: New music: Songs where one or two members love these enough to teach them to the band and work them if/as quality warrants. Sometimes these are chick songs, drinking songs, hard blues, etc.-- the spice in the mix to use sparingly, and/or where one or two can solo/duet while the rest of the band retunes, takes a short water break, takes a leak, tweaks the sound system, etc.
C list: The ones the crowd will love that are not too hard for the band and that can fill in the middle parts of the sets

And at least half of these have to be fun to rehearse. More if possible.

Part of the rehearsal is revisiting well-known pieces to keep them fresh, then move on to the ones that are new and a little friustrating, then close with the C-list stuff. ALways begin and end with the stuff everyone will feel good about.

In rehearsal, unless it's a DRESS rehearsal, don't worry about nailing down arrangements, who will do what, what will happen in an instrumental or vocal solo break, etc.. Keep a loose hand on the rehearsal till the whole band feels a consensus while playing, and the songs COOK.

~S~