Ive put this one up before, Sit on a stool with jab shoulder against walllooking along the wall. Throw the jab with the arm never leaving the wall and turning the fist as you do also pulling the back shoulder back as you do it keep repeating for half a minute youll feel it in the shoulder rest and repeat it will give you a terriffic jab it makes the muscles work correctly and it will be biomechanicaly correct.