Now that I've written down what I've been doing with the improvisation group it's easy to see what I've been doing wrong. Some of it, anyway. No doubt continued documentation will uncover further errors.
1. No matter how much fun it is to join in, I need to stay out of the exercises and observe. How can I analyse anything when I'm in it up to my eyebrows?
2. I need to keep it simple, and explain the rules of a game very clearly.
3. I need to give each exercise time to breathe, not move immediately on to the next.
4. I need to know, at least roughly, what each exercise/game aims to develop so I can assess how well it's working for us.
5. I need to slow down and pay more attention.
6. I need to be in charge. Friendly and informal, yes, but not wishy-washy.
7. I need to establish some ground rules, some discipline, about how we work together. The more seriously you take it, the more fun it is.