My archery instructor as a kid was a master archer and he used to have really good solutions when my shooting was bad.
The bow shooting technique was to use a bow finger sling on your hand with the hand holding the bow. I was a lefty. You're not supposed to grasp the bow real tight just hold it in place when you release the arrow and the bow gets held up with the sling so it doesn't drop when you release, but I would always anticipate and grab or throw the arrow off. What my intructor did was put some tacks through a peice of tape and tape it to the front grip of the bow where my fingers would grab it. That way I wouldn't flinch or anticipate. I'd hold it steady each time. It seems kind of cruel but it worked.
I don't know if this will help with gun shooting though.