If you are restricted in your neck motion, you most likely will take your eye off the ball or have an abbreviated shoulder turn resulting in faulty body motion and swing mechanics. Freeing up your neck will help you make a complete shoulder turn and take your muscles through the full range of motion.

Stand or sit on an exercise ball or chair with straight posture.
Slowly drop your chin to your chest and then circle your head clockwise, taking your neck through full range of motion.
Circle your head clockwise for 8 to 10 repetitions.
Repeat rotation counterclockwise for 8 to 10 repetitions.
Stop if you feel dizzy.