Players 1 and 4 dribbles the ball to the free throw line and passes the ball to the person standing on the side of the court, who immediately throws the ball back. The player then dribbles to the half way line and repeat. The players on the other side are repeating the practice going the opposite direction.
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.