Receiver faces three players who one after another spikes the ball for it to be digged. Change roles after the player has faced 3 spikes from each player.
Don't allow the player to wait between spikes. The receiver must be ready at all times to react to the ball.
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.