In longer projects, I may ask the teams to designate roles for each person. This would include giving a presentation in class. In shorter projects, I tell the teams to divide up the tasks any way that works for them, but that everyone must understand everything. I roll dice to determine who speaks for the class presentation on presentation day. In order for anyone to do this, the students generally spend time preparing props and charts.
Students take responsibility for the inter-personal issues and project management issues.
Students learn from each other. There is also the phenomenon that individual students may demonstrate unexpected talents. The class work sessions require me to do the group assignments on the spot so counting off or names out of a hat or using their ID numbers or e-mail numbers are best. I use rubrics for projects. Throwing dice to determine who presents is something students enjoy.