HOW: Get set-up next to a wall or doorway and place your hand on the wall down by your pocket with your palm against the wall, there should be some space between you and the wall. Focus on keeping your shoulder and shoulder blade in a good position by keeping it back, then perform the pec stretch by leaning your body forward and maybe rotating your chest away from your hand. While holding this position, rotate your head away from your hand as far as you can, return to starting position and repeat.
FEEL: You should feel a stretch in your pecs, the front of your shoulder, and maybe your neck as well as some tension on your nerves in your neck/arm when your head is fully rotated away. You shouldn't feel any numbness or tingling or pins and needles in your arm/hand or worsening of these symptoms if you have them, if you do back off.
COMPENSATION: Try to focus on just rotation, do not side-bend your head and neck. Don't let your shoulder fall forward, keep your shoulder blade back.