Successful pitchers are all able to generate major velocity numbers. This is an important factor that starts with your training. Being able to train and gain strength to throw the ball hard is going to put you at an advantage over the hitters. 

Being able to control the ball is a very important thing. No matter how hard you throw, if you can't locate the ball it wont matter. Being able to throw strikes and compete with the batters is how you are going to shine as a pitcher.

There are many different pitches that are used. Being able to throw off-speed pitches for strikes and keep the hitter off balance is the key to having success.

The ball has seams on them, based on how you grip the ball using the seams is going to determine what the ball does on the way to the catcher. You can throw curve ball by having your fingers on the right side of the seams and changeup by gripping it wider on both sides of the seam. 

Being confident in all the work you put in is going to make you the pitcher you want to be. Confidence plays a huge role and is needed for you to attack the hitters and get them out. You can't be scared to throw a certain pitch and have to trust everything you do.