Focusing on core muscles can help you develop strength and speed for more power in your golf swing. Doing this exercise in your golf posture, as you engage your core muscles, can improve your swing mechanics as well as core strength.

Stand in your golf stance holding an exercise ball with your arms extended as if you were holding a golf club.
Slowly begin rocking your shoulders back and forth as if you were swinging a golf club. Use your shoulders to turn, moving your torso back and forth, keeping your lower body stable.
Squeeze the exercise ball as you swing it back and forth to, not only engage your core muscles, but to also increase strength in your upper body.
Rock the ball back and forth for 8 to 10 repetitions on both sides.