I apologize that it has taken me this long to respond to your initial message. I have not been very involved with this network, I am hoping to change that. I'm working on updating more information and learning more about AIN. Looking forward to hearing from you!
Marv, I like to start with simple improv exercises that are low risk, like word-at-a-time story in small groups, or Mirroring in pairs. After everyone is more relaxed, you can then try inviting a few volunteers to come up in front of the group for some other exercises. The improv games I use depend on the purpose of the talk.
Good luck! -Yael