Place the cues for an overhand serve in the correct order. Dominant arm/racquet arm back behind your ear.

Non-dominant foot forward.

Toss ball in front of server slightly above your head.

Strike with heel of palm/racquet.

Follow through (arm across the body).

The person who utilize the progression principle will keep adding the difficulty of the exercise that he's doing, while the person who does not, will only stay stagnant.  the person that utilize progression principle, will get a stronger endurance because now his body is conditioned to do harsher routines.{the answer was already on verified)