Find a flat platform that your players will easily be able to jump onto and then have a controlled landing when they jump off of it (a gymnastics vault box is ideal as the height can be adjusted for the level of your players).
Once the player is on the box, they gently jump forward off the box.
Make sure the landing is controlled.
You don't want to be falling forward or leaning back after the landing.
Progression:
As soon as the player hits the ground after jumping off the box they should jump as high as they can off of both feet.
Rebounding is the least glamorous thing in basketball and one of the most decisive. It is also almost entirely a habit, which means it is entirely coachable.
Good spacing is only the start. The best modern offences teach players to attack the defence's rotations and play in a permanent 4-on-3 - here is how to coach that read.
The ball screen produces almost half of all professional offensive possessions, yet most teams still teach it as a memorised play. The modern approach trains the read - giving players a framework to decide based on what the defence does, not what the coach called.