Brainstorming is one of the most commonly used group decision-making techniques. It is designed to generate a large number of creative ideas through an interactive, inclusive process. A brainstorm starts with a clear question, and ends with a list of ideas. That's what it does well - give you a ‘raw’ list of ideas. Some will be good, and some won't. But, if you try to analyze ideas in the brainstorming session, you will ruin the session. Wait. Later, you can analyze the results of a brainstorm with other tools. In particular, Affinity Diagrams are designed to sort a raw list, to begin to categorize these ideas.
A Structured Brainstorming can sometimes help a group get into the idea of brainstorming or can ensure that all members get a chance to provide ideas. It can be done as a round robin, where participants take turns shouting out ideas, passing when an idea does not come to mind quickly. Another way to ease into the technique is dividing the group into small groups of three or four. Brainstorming is done in this smaller unit, with all ideas generated being shared with the whole group later.