Put Your Shoulder Blades In Your Pockets.

The best cue I've ever heard for how to prepare for many lifting, pulling, or pushing movements is to put your shoulder blades in your back pockets.

This is important because it gets your back and shoulders set and ready to do their job. On these movements, the arms and legs are what should be doing the moving. If you are doing a pushup and your shoulders are moving around a lot they are doing a job that isn't theirs. It is like a workplace in which somebody never does their job, and so the people around them have to pick up some of his/her responsibilities. Just as this leads to a dysfunctional workplace, allowing other muscles to take over the jobs of the prime movers leads to dysfunctional fitness.

When adopting a new exercise, or program it is important to know which body parts should be doing the work as well as to make sure that those body parts are actually doing the job rather than other parts.

A big part of my job as a personal trainer is to make sure my clients are doing their exercises properly. Doing the exercise correctly strengthens the right muscles and avoids injury from contraindicated movements.