Pitchers should break their hands directly in front of their bodies, preferably up around the letters. First, the throwing arm will often stop after the break to allow the lead arm time to catch up, ruining a smooth, continuous circle action with the ball after the break. Second, the lead arm does not get to the bridge position soon enough, and often arcs out away from the body instead of moving directly toward the target. This arcing of the arm and the time it takes to bridge can throw the lead shoulder open way to early. When the shoulder opens before the lead foot is planted, velocity is reduced and arms can be injured.
Many young pitchers have difficulty with balance.
One of the reasons is poor mechanics at the beginning of their windup. The reasoning for this is that you want the pitcher to take his weight straight back so that all of his weight is coming forward toward the plate when the pitch is delivered. The pitcher's weight should be back when the front knee is lifted and he should be able to balance on one leg. Importantly, the pitcher should try to keep his head and weight over his front foot. This will allow him to make a smooth and balanced pivot into the knee lift part of the windup.