You never want to lunge at the ball when shadowing a dribbling ball carrier.
Keep one foot on the floor at all times and keep your balance. So if your man catches the ball you can immediately to an on the ball defensive position.
Glide out to the side line and back to the block.
Do this three times, rest and repeat. Do another three then repeat on the other side.
This can de done in pairs or individually as a simulation drill.
Keep body low.
Feet come together but do not cross.
One arm down and in front to prevent the cross over dribble.
The other hand down and in front to prevent the pass.
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.