Jared Zak: How to Launch It (May 2014)
To increase your clubhead speed, pay close attention to the relationship between your upper body and lower body, especially on the downswing. The longest hitters start down by shifting and rotating the lower body independently from the upper body: The upper body stays back as the lower body moves forward. This causes the shoulders to tilt, with the right shoulder below the left. This combination of body separation and shoulder tilt is what slings the clubhead through impact with maximum speed.