Creative sessions are all about good vibes, concentration, right mindset and expertise. These are all very different factors that can be decisive for the outcome. You want to make sure you choose the right people to contribute to your ideation session.
It's impossible to find a fixed rule on how to select the perfect team, but here we name some points you might want to take in consideration.
Have a good ratio of rational and abstract thinkers
Some people find it very easy to come up with out-of-the-box ideas, while others are better at pointing out realistic solutions. Mixing these two kinds of thinkers is crucial to get original ideas that will work. If you have only one of these types, your concepts will be too crazy or too dull.
Include an expert
Get at least one person that knows a lot about the issue/project you are facing. This person will add experience and critical thinking.
Include an outsider
A project manager, the receptionist or the intern. Whoever that person is, s/he should start from zero without knowing much about the project. That will bring fresh energy to the room.
Push for diversity
Different backgrounds and ways of thinking will add new perspectives to your process. If you have the same type of people in the sessions, your solutions will always be the same.
The right amount of people
More people won't mean more ideas. A big group could mean miscommunication and more energy to manage it. Be careful with the number of members you bring.
Have a facilitator
We talked about it before. If you haven't read it yet, go and do it :)