Pitching is extremely important in every game, especially Baseball Stars, where most games are high scoring. Having a good pitching strategy can, and often will, be the difference between a win and a loss.
Move around on the rubber. It helps you get a head start on where you want to curve the ball.
Don't overuse your fastball. It isn't all that important when facing a computer-controller opponent. All it does is wear your pitcher out much faster.
Don't overuse your drop pitch. The more often you use it, the less likely it is to work, and the less likely opponents are to swing.
Don't leave a pitch over the heart of the plate unless the opposing pitcher is batting.
When facing power hitting teams, take your pitcher out immediately when he shows signs of fatigue. If you don't, you could see a few runs go on the board pretty darn quickly.
If you are facing an extremely tough hitter, there's a way to strike him out. First, throw as far inside as you can without hitting him. Then, throw over the outside corner. If done properly, the hitter won't swing at the strike on the outside corner because his bat won't be able to reach it. Repeat three times and you've got a K.
The scouting reports in this shrine work. Use them to your advantage.