Here is a great shooting drill to help you work on shots off the move.
It works best if you have a Gun, Shoot Away, or an extra rebounder as well as a passer.
Just follow the pattern shown in each of the frames and make sure you pivot on your inside foot as you prepare to shoot.
The cones can be moved closer together or farther apart depending on the size and strength of the shooter. (It is best to start with the cones closer so the shooter can experience some success before moving out towards the 3 point line.)