To gain control, you must first give up control
Ok, I know it sounds like something out of the movie Mystery Men. That’s no accident. But it really is true.
All too often, pitchers (especially beginners) will try gain control over their pitches by consciously trying to guide the ball to its intended location. The problem when they do that is they end up tensing up, and essentially guessing how to position their bodies, when to release the ball, where their hand should be pointing, etc. At that point instead of improving their control, their bodies are actually working against them and control gets worse.
To learn control, pitchers need to let their bodies relax, work on their mechanics, and let the ball go where it may for a while. In other words, instead of trying to guide the ball to a specific spot they should work on acquiring the proper mechanics to throw a ball to that location — whether they actually get it there or not. For example, when working on throwing to the glove side or throwing hand side, the focus should be on stepping slightly left or right (if that’s the method you use) and following the body with the arm circle rather than trying to “aim” the ball at the end.
Remember that control is not a goal. It is the result of doing things right. So if you really want to gain control, first give up the desire to consciously control the ball. Let go your conscious mind and let it happen organically. You’ll get where you want to go a lot faster.