After a shot is released move quickly to a re-rounding position and put back with a power move.
Remember to open out to get more reach.
Go up to the shot from the chin position. Do not take the ball outwards then up.
Do twenty of these on each side.
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.