Tricep stretching should be done after triceps workouts, shoulder workouts, or chest workouts (all involve triceps work!).
With your back straight, place one hand behind your back with your elbow straight up in the air as if you are trying to scratch the middle of your back.
With your other hand, press down on your forearm to accentuate the stretch.
Hold this for about 10 seconds then release and switch sides.