This chest stretch is one of the easiest ways to elongate the pectoralis muscles in the chest. It can be done before and after workouts that involve pushing exercises like the pushup.
To do this stretch, place your forearm at a 90 degree angle against the corner of a wall, or sturdy column. Keep your forearm against the wall and lean forward gently with your bodyweight. As your arm goes farther backwards, you should feel a stretching sensation increase in your chest muscles and the anterior side of your shoulder.