You must start with a clear understanding of the problem at hand.

• Why are you setting up a brainstorming session?
• What is the problem you are trying to resolve?
• Who does this affect?
• Who needs to be involved?

Once you have clearly understood your problem, describe it in the invitation email so participants can come mentally prepared.

Can you reframe the problem in several different ways? This could spark off new ideas inside participants' heads before they turn up!

Note: there is no "How?" at this stage. The brainstorming sessions will start you down that path.