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 should turn around, step off the box and then, as they hit the ground, jump as high as they can off of both feet.
Make sure the landing is controlled.
You don't want to be falling forward or leaning back after the landing.
Good team defence is five players guarding the ball, not five separate one-on-ones. The shell drill is where that starts, so here is how to teach help-side positioning and rotations from the first week of the season.
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.