A well-facilitated brainstorming session is like a symphony -- or, at the very least, a really good performance of any kind of music.
Embedded in its DNA are dynamics (i.e. "variation and contrast in force and intensity") -- the skillful modulation of elements that fully engages a person's attention.
The opposite? Muzak.
Next time you listen to a piece of music, be aware of dynamics -- the various ways in which the composition holds your interest (i.e. rhythm, pauses, crescendos, harmonies, solos, and multiple variations of soft and loud).
As a brainstorm facilitator, you need to do everything in your power to keep the session as dynamic as possible so participants remain fully engaged -- poised and ready to respond.
If the session is boring (or takes a "dip" after a brief period of engagement), your chances of succeeding decline exponentially.
Towards this end, think of yourself as a "conductor" -- the one who guides a group of individual contributors ("soloists") through an artful process that ensures a quality experience and a meaningful outcome.