I like to begin “brainstorming” sessions with some kind of low-stakes improvisation activity. This forces participants, from the beginning, to think outside normal boundaries. I also use this step to provide additional context for the remainder of the brainstorming session.
After the improv, the next step is to present the focus or core idea of the session. The goal here is to provide clarity and any process guidelines for the brainstorming.
At this point, I have people work in groups and work through three different idea evolution phases. This begins with brainstorming real-life examples of the idea that have been successful. In the next phase, the groups brainstorm possible scenarios for applying the idea to their specific situation. Finally, I ask the groups to brainstorm actual solutions that contain the best elements of their previous two rounds of discussion. In each phase, feedback from group members helps refine and prioritize contributions.