There are a number of different pitching drills pitchers can do to improve their performance. Many of them involve being on the mound, and others involve being off to the side.
For instance, there is the towel drill. Where a pitcher will hold the towel between the pointer finger and middle finger, go through his delivery, and smack down upon a partners glove, or a bucket to work on an effective follow through upon delivery.
Another effective pitching drill is long toss. Where pitchers start at 50 feet apart, and progress further and further away, until they're 2 to 300 feet away from each other, extending the distance of throwing that long toss.
Another drill is spot drills. In spot drills, pitchers will partner up from 20 to 25 feet away, and work on throwing a fastball, curveball, and change up from 20 to 25 feet away to a partner.
Another effective drill would be therapeutic bends. Therapeutic bends enable pitchers to improve their arm strength, and maintain a healthy arm by doing a variety of drills, including internal and external rotation.
The balance beam drill is a drill in which pitchers will balance themselves, either on a balance beam, or a bleacher, and hold the balance point position to master effective fluid balance point.
The ball up drill is a drill in which pitchers will watch their arms as they release the ball from the glove, or separate their hands, and get into an effective arm. Pitchers can do this in front of a mirror, or watch as they lift the ball above their shoulder in various grips.
Medicine ball drills will enable pitchers to incorporate their hips more effectively in their delivery, and allow them to pitch deeper into their games, as well as, throw higher gun speeds on the radar gun.
Pitching drills are the key to becoming a better player. It's not enough to throw off the mound in a game or practice. Pitchers can work on these various drills to improve their performance, to achieve higher pitch velocities, and better command of each of their pitches.