Anytime you can, go through your shooting motion. Remember to use basic shooting technique (elbow in, follow through, smooth release, elbow at a right angle, off hand guiding the ball, et cetera). You do not need a ball, just imagine you are holding a basketball and shoot just like you would on the court. This may look strange in public, but this drill combined with practicing on a real court will make your shot more fluid, increase accuracy, help focus, and overall make a jump-shot seem like second nature.
If on a court, stand at many different shooting spots on the floor. Try to store this images in your head so that when practicing this drill, you can imagine you are shooting at the goal.
Practice, practice, practice (and make sure you are practicing shooting technique correctly).
This very easy drill can help improve shooting form.
Shooting technique, focus.
1

The basketball drills are licensed under a Creative Commons License.
TLC: Pål Degerstrøm 2000-2008