First of all, I feel the need to explain "rehearsal" in the context of improv. Improv is totally made up on the spot, with no way of knowing what the audience will suggest or what your scene partner(s) will say based on those suggestions. So we clearly can't rehearse scenes. Duh. That would be called acting.
But in short form improv, there are a variety of games (you've probably seen 'em on Whose Line) like New Choice or Playbook or Foreign Movie that we play, and it's helpful if the improvisors understand the games before showtime. Just think of rehearsal as football practice: you practice the fundamentals so when the big game comes along, you know what you're supposed to do. You still don't know if the other team is going to blitz, or if Tim Tebow will suddenly learn how to pass, or if your kicker will make the easy 38-yard field goal, so you can't preplan your specific moves. But you understand the game, so you'll know what to do in any of those situations.
Anyway, the reason I look forward to rehearsal so much is because everyone tends to be slightly amped for the upcoming show, but still loose and relaxed because there's no audience. That combo of high energy with fearlessness and the joy of playing with people you know and trust leads to great improv. If you eff up in rehearsal, so what? But precisely because you're that bold, you probably won't eff up, and it's so much fun to see people playing that confidently.
That's how it is in Held2gether improv classes - the level of trust and encouragement makes everyone feel comfortable being bold and creative and adventurous, and pretty soon you're addicted to hearing people laugh and applaud. Which is a pretty good addiction to have, if you're gonna have one.
Um, there's no moral to this story, actually. Just sign up for an improv class already, would you?
By Sonnjea Blackwell