Two balls per player, who is laid on his/her back.
One ball is kept in his/her hands which are held with straight arms behind/above their head, the other ball is kept between the ankles.
The player then brings his/her legs up as vertical as possible, keeping their legs straight and the ball in control between their ankles.
Once a player lifts his/her legs to around 90 degrees to the hip joints, he/she reaches to touch the ball in their hands with the other ball. After that goes back to laying flat on the floor.
In this drill the abdominal muscles and leg muscles are strengthened.
This will help build a player's core strength which is needed to develop better balance.
To introduce advanced balance ask players to elevate all limbs at the same time.
New hitters rarely miss because of their arm. They miss because of their feet. Build a reliable approach, then time it with your setter.
When your hitter gets stuffed, five teammates standing and watching is how you lose the point. Good attack coverage turns a blocked ball into a second swing.
Coaches spend hours correcting arms in serve receive when the real fault is almost always the feet. Fix the movement and the platform fixes itself.