Try having 2 sets of stumps around 15 metres away from each other, as you would in a normal game (Apart from the decreased distance). Have a wicket keeper stood behind the stumps at the bowlers end, with 2 queue's each side of him, square-on with the stumps. And another queue behind the 'batting end' stumps.
The wicket-keeper starts of with the ball (Tennis ball, windball, incredairball etc.) And rolls the ball to his right, the first person in the queue picks the ball up one-handed and using an underarm throw aims for the stumps. The first person in the queue to the left of the wicket-keeper picks up the ball two-handed, and has an overarm shy at the other set of stumps. The people in this queue pick up the ball 2 handed and throw into the wicket keeper, and the process repeats. After a person has had their pick up and throw, they move to the next queue.
You can develop this by taking away stumps to aim at (If using kwik-cricket stumps), changing the ball, using left hand only, changing the ball, 2 balls on the go etc. etc.
Hope all that makes sense! It usually works well as you can using for a group of around 8-18 people, and focuses on all different aspects of fielding.