This exercise is best done with several trainers (e.g. trainer + assistant trainer) and space in the gym.
All players have their own ball. Throw the ball, test it and catch it yourself.
Good X number of times, then move to field 2.
Coach throws ball over net. Player keys and catches ball.
Player retrieves ball, puts in trainer's basket and connects again.
X number of good shots + catch (judged by trainer), then move on to field 3.
Trainer throws ball over net. Player tests, catches and throws ball back over net. Throw ball into the ring/on the mat on the other side of the field.
Retrieve ball by yourself and connect.