The essence of brainstorming is that production and criticism of ideas are kept separate. To encourage divergent thinking in group problem solving, participants are encouraged to produce as many ideas as possible without fear of criticism or evaluation. Only after a brainstorming session is complete are ideas reconsidered and evaluated. As ideas are freely generated, an interesting cross-stimulation effect takes place in which one participant's ideas trigger ideas from others. Criticism of an idea is absolutely barred.
All evaluation is to be deferred until after the session.
Modification or combination with other ideas is encouraged. Don't worry aut giving credit for ideas or keeping them neat. Quantity of ideas is sought. In the early stages of brainstorming, quantity is more important than quality. Try to generate lots of ideas.