Discussion of the art and craft of improvisation.
Creating or rehearsing a specific format gives you the tools to be able to make a better, more varied, and more interesting moves in an open show. Just saying "anything goes" at the beginning of a show tends to end with people defaulting to what they're comfortable with. Even if you don't take a specific format to the stage, I think it's invaluable to rehearse very specific and comfort-pushing things in rehearsal.
Parallelogramophonographpargonohpomargolellarap: It's a palindrome!
I like thinking about what kind of story i'd like to tell, either influenced by genre, a specific property, an atmosphere I want to evoke, or some particular plot shape/structure. something else that's come in handy is focusing on one particular element in a show (character, relationship, theme, setting, dialogue, edits, blocking, stage picture, etc.) and deconstructing it in rehearsal, just exploring it from every angle. eventually, you trip across something that makes you think "well, THAT would be fun to do onstage!" or at the very least gives you a seed that starts developing into something else, especially with everyone else's minds engaged.