The roles are clearly defined in advance, so that each person is accountable, and everyone in the group plays an important part. Seats face one another. When students face their coworkers, they are more likely to interact well with others. Seating arrangements really do make a difference, and sometimes students need to be reminded that they should move chairs closer together or place them in a circle. You can set up the room with seats in clusters to facilitate this process.
Students assume personal responsibility.
Invite students to report back to their group or to another group after each session. Give clear guidelines on paper for each person's role and go over them, so that students understand the criteria for his or her role. Change roles regularly, so that students can learn to assume responsibility in a variety of areas. Students relate well to others. Some students are better than others at interpersonal exchanges.