The four requirements for an effective brainstorming session are:
1. Create a comfortable and open environment where everyone feels safe to share their ideas.
2. Encourage active participation from all team members by providing equal opportunities for contribution.
3. Set clear goals and objectives for the brainstorming session to keep the discussions focused and productive.
4. Use brainstorming techniques such as mind mapping, storyboarding, or SCAMPER to stimulate creativity and generate a wide range of ideas.