The best tip I can give, is Stretch all the muscles that are used for the movement of the jab. Which incorparates a large area, it will make the movement biomechanicaly sound. It will give you good practice. Understanding Feel is a two way thing as regards your practice, its adaptable muscle, it the movement can be wrong, but if thats all it knows ,then theres a problem. Theres injury waiting to happen. Wrong its already happened.