Progressions play a big role when it comes to challenging the athlete from one phase to the next. Not to be overlooked, regressions play just as important a role because any progression may need to be, in fact, regressed…that is made simpler. Some sample progressions for training can be…
Static–>Dynamic (front plank–>front plank march)
Increasing the Range of Motion (DB Reverse Lunge–> DB Reverse Lunge from a deficit)
Wide to Narrow (decreasing base of support)
Stable–>Unstable (Push Up on ground–>Push Up off Bosu) **only applicable in upper body lifting
Acceleration–>More Deceleration Oriented (Reverse Lunge–>Forward Lunge)
Check out this holy grail of the basic movements that most will have success with in my opinion.