The most important thing with brainstorming is to let ideas flow and the wilder the better. Try using a white board to write down all ideas and then transfer them to a note book or word document. Some of the best stuff that kids use later may come out of these sessions. Your role as a coach is to record it all and provide guidance on how to record the info, not what to record. Later in the season, teams will forget some of the coolest things they thought of earlier, but if they can go back through the notes they will locate some awesome ideas.