Grip the ball deep in your fingers, not in your palm
Place your thumb underneath for support
Hold the ball with a loose, relaxed grip
Keep the same arm speed as your fastball
Stride and throw with normal mechanics
Release the ball with a slightly slower wrist action
Let the ball come out off the fingers, not a push
Maintain good arm action to disguise the pitch
Aim for a lower velocity than your fastball
Practice the grip and release repeatedly
Focus on control and consistency
Throw it in game situations only when you can command it