Players stand on the attack line facing the net. If the player is right handed, they start with a left leg step, followed by two quick right-left steps and then jump.
While approaching to spike, the last step should be performed with the left foot (right-handed players) so it would be positioned a little bit in front of the right foot. It helps to rotate shoulders and hips which are then re-rotated while hitting the ball. Torso generates additional power which joined with hitting arm power makes kills ultimately powerful.
To improve arm-leg coordination you may ask players to become left-handed for a while and try to approach with right foot step as last.
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.