Take a tennis ball and place it under your armpit. Now roll a few times back and forth and use this hand to do regular jobs like opening doors, reading and picking stuff of the ground or tray. Now place the ball between your neck and shoulder and repeat this drill and than remove the ball altogether. Now have a partner come at you with a knife stabbing and you will move away with the body and conceal the blade and guide it adding your limbs to the work. Later on you can add slashes and other moves but remember to flatten the blade on the body and to work with the person without putting all your focus on the knife. It is a tool.