I’ve seen this all too often—pitchers who throw with all arm and don’t use the lower half of the body nearly enough, if at all. Let me tell you about what I used to do in my playing days, something that goes way back.
What I found out, early on, was that pitchers need to get the whole body into the action. I used to go to Yankee Stadium every chance I got, and I would watch the Yankees’ Big Three in action—Allie Reynolds, Vic Raschi and Eddie Lopat. I watched them during pregame practice and in games, and I noticed that they were all doing the same thing; they were driving off the lower half of the body, using the legs, the hips and the torso in one continuous motion, and that was how they were generating the power behind their pitches. They were all using that seamless motion to create a nonstop flow of energy from the bottom all the way up through the shoulder and the arm to the fingertips, so they could throw harder with less effort—even Lopat, who was by no means a fireballer. What this did was take a lot of pressure off said arm and shoulder. How not to get a sore arm.
I made a note of this, saw exactly how they were doing it, and started working on it on my own; as I practiced this essential element of good mechanics I found that I was doing the same thing they were. I can tell you about one thing that should get you started: it’s called the “Hershiser” drill, and it aims to get the hips fully involved—the hips are actually the connecting point between the lower and the upper half of the body, and when you can get everything working together you just might find yourself with more power to spare. And the “Hershiser” drill requires no special equipment, just a fence or a wall. You can find it on this website, with instructions on how to do it.
As for throwing strikes—here’s something else I used to do in my playing days. I would get a catcher, we would go to an unused playing field, I would take the mound while he set up behind the plate with his mitt, and we would play a little game we called “ball and strike”. He would position his mitt in different places: high, low, inside, outside, on the corners, everywhere except standing on his head, and I would work on getting my pitches smack-dab into the pocket of said mitt. I don’t know what your arm angle is, but I was a honest-to-gosh sidearmer and I used the crossfire a lot. It was a terrific workout and a lot of fun, and i can’t think of a better way to sharpen up one’s control! 8) 
