If you have a hard time making a complete shoulder turn or you take your eye off the ball, then you may need to improve range of motion in your neck and shoulder area. Lack of flexibility in your neck area may result in loss of spine angle, faulty clubhead position and lack of timing.

Stand or sit on an exercise ball or chair with straight posture.
Slowly side bend your neck to the right bringing your ear toward your shoulder as far as you can, hold position for a moment and return to the start position.
Repeat motion on opposite side.
Alternate bending your neck side to side for 8 to 10 repetitions on both sides.
Be careful not to allow your shoulder to raise up.