Warren Spahn said, “Hitting is timing. Pitching is upsetting timing.”
All pitchers need to have a pitch they can consistently throw for strikes. This is usually a fastball. To really be successful, a second pitch needs to be developed that can be used to mess up the hitter’s timing.
Smart coaches and players will watch pitchers to see if they are tipping their pitches. Be sure that your motion and arm speed are exactly the same no matter what pitch you are throwing.
Work on your off-speed pitches. Play catch using your changeup grip. Develop enough confidence in your changeup that you can throw it in disadvantaged counts (1-0, 2-0, 2-1, 3-0, 3-1).