2 players, 1 ball. The player serving has to hit the ball over the net so that the other player can catch the ball.
If they are successful 3 times in a row the player can take a step back and move closer to the back line.
Once players reach the back line they can swap roles.
Control the weight movement from back to front when serving.
Look at the tension in the hitting hand (should be like giving a high five).
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.