Recruit participants with class, race, age and other diversity in mind. Reach beyond the usual suspects, and keep extending warm one-to-one invitations.
Meet someplace comfortable, with snacks or a meal.
Appoint a facilitator for each session who will pose the questions, keep the discussion on topic, and encourage quiet people to speak.
Make a clear agreement on commitment to preparation (reading or watching ahead of time).
At the first session, get group agreement on some groundrules.
For example:
Listen to each other intently. Bring an attitude of respect and curiosity.
Step up, step back: Talkative people hold back, quiet people speak up.
Confidentiality about any personal or organizational sharing.
Disagreements are fine; personal putdowns are not OK. All questions are good questions.