I wanted to write this in order to remember several of Maggie Nicols' exercises that stuck with me. I thought they were great ways to introduce controlled improvisation to a group.
One is to start with only a short sound, a single syllable at any pitch or dynamic (we all sang the syllable "bop"). In the beginning there is silence, then anyone is free to give a starting impulse by singing his/her "bop". All immediately follow, singing their own short "bop". It will (and should) sound like a scattered cloud of notes. Then silence, then someone else (anyone) starts the second cloud of short sounds. This goes on, someone giving an impulse, others following, always with silence afterwards. After the fifth impulse there can be more freedom to develop, let things happen, sing longer notes, lose the silence, etc.
Since you have a parameter of one syllable there is no worry "oh, what am I going to sing!?" It's just "bop". Hooray!
For this next exercise we split into trios. We were all free to sing and vocalise what we wanted, the only rule was that if someone stopped, we had to stop too. A wonderful way to exercise absolute freedom combined with the responsibility of listening carefully.
Some of the social implications of these exercises interested me, since I am often bothered by the line between strong individualism and social consciousness. Maggie Nicols pointed out the importance of allowing absolute freedom of expression. If it is withheld, the repressed start to look cattily at those who express themselves freely. No one needs that.
How do you exercise responsibility within this freedom? Well, in music, it is relatively easy, just listen.