I would also add that having contributors - people who address the topic and honor the people around them rather than steer the conversation to themselves. There are some people who can't help but to start every sentence with the word "I".
another edit (as I read): In an article Mel Brooks described the writing at Your Show of Shows: They constantly reworked the same scene until something really great emerged. The writers felt like they belonged to something greater than themselves. Critics and TV historians call this comic gold. I call it “group flow.”
One thing I want to add that I haven't seen yet is that the people in the group have to believe in an idea. Too often I am thrown in a group forced to explore an idea that doesn't apply to me.
Another huge problem is where o you find a group??? In hinting this idea around, people are satisfied going about their merry little way and nobody is interested at all. Seems like everybody needs an activity - poker, drinking, restaurants. Considering so many people waste so much time, they are quite protective of 120 minutes once a month. Not that I have outrightly invited anyone yet - but I get a feel for these things. Haven't found anyone right for it yet.