Players work in pairs facing each other.
The player opposite starts with the ball and underhand passes it to their teammate, who takes flight off of their front foot, and digs the ball at full force.
The ball should be thrown at a good height to enable the player to dive properly towards it. The knees should not make contact with the floor on landing.
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.