This exercise randomly selects group members. You will need as many ping pong balls as you have people. Decide in advance how many groups you want and how many people you want to be in each group.
Prepare the ping-pong balls by writing a group number on each ball. For example, if you have twelve people who will be working in three groups of four people, then write '1' on four of the balls, '2' on another five balls and '3' on the last five balls.
Throw the balls to the participants until everyone has caught or retrieved a ball. Then ask them to work with the people who have the same-numbered balls as themselves.