After conducting their user and design research, participants should initially sketch alone. You want to ensure each person gets the opportunity to be individually creative. Plus, you want to produce enough sketches to get out of the common response zone, to create something that is innovative, inviting, and intriguing.
“Artists work best alone. I do not believe anything really revolutionary has been invented by a committee.”
— Steve Wozniak
While your Sketchers perform user and design research, you should remind them of the Four Rules for Generating Ideas and the 10 Rules of Sketching.