If you want to make your swing longer and create more club head speed, you have to make sure your shoulders bend the correct direction. At the top of backswing, try to feel like you puff your chest out and point it more skyward. This would create a backward bend necessary lengthen your swing.
Your follow through is the same. If you bend the shoulders back and point your chest more up to the sky in your follow through, you can maintain an in to out path more effectively and extend the arms toward the target longer for better speed.
Tyler Raber