It is important to turn your torso independently from your lower body to create a spring like effect in the backswing. Plus, in order to sequence your downswing correctly, you need good separation between your upper and lower body.
In order to create this movement, you need to have sufficient mobility in your thoracic spine, as well as stability in your hips. This exercise will help you increase your rotation in upper torso and separation between your upper and lower body.
High Rotators with Exercise Ball-
Hold an exercise ball, hand weight or golf club between your hands with your arms extended. Stand in a shoulder width stance.
Keeping your lower body stable, rotate the ball to one side, keeping your arms extended and twisting from your waist. Turn as far as you can without shifting your weight.
Return to the start position and repeat on opposite side. Do 8 to 10 repetitions on both sides.