"Concentrate on the correct movement every time you exercise, lest you do them improperly and thus loose vital benefits" Joseph Pilates
My favourite principle!!
The brain gives the command to the muscles to move, if you want to move in the correct way, you mind should be fully awake and present. Always send your mind to the part of the body that is moving and think about what bones are moving and what muscles are contractive, you will optimise your experience and take the most out of a specific exercise.