In short: practice various forms of the shot in a fun competition format.
Organisation:
Each group has a basket and a ball, the baskets should preferably (but not necessarily) be arranged in a circle or rectangle.
The number of people per group is less important (all groups should be about the same size).
The first assignment for the groups is:
score 10 goals with a walkthrough.
When you are done, the creator of the last goal goes to the trainer to get the next assignment.
Which group will have completed all assignments first?
The trainer walks around in the mean time,
giving encouragement or correcting here and there.
He has a piece of paper with a list of assignments.
When someone comes to get the next assignment, first ask him which assignment he just did (it can vary a lot after a while) and then give the next one.
A sample list:
10 passing balls,
15 penalty shots,
10 shots from 5 meters,
10 through balls from behind the basket,
5 dodge balls next to the post,
5 shots from 4 meters behind the basket,
5 small chances with 1 hand.
Everything is possible of course, a lot of momentum comes when the number of goals to be scored is kept small.