Master Balance & Posture
Balance and Posture are very important to the success of you swing. If you have poor balance you will have to catch yourself as you move the club back and through. If you have poor posture it can cause you to sway and have a poor rotation of the torso, which will lead to poor path, and a loss of power. Work from the ground up to get into a stacked position.
Feel the weight balanced across the entire foot as if the arches of your feet are pressed into the ground. You should feel the weight on the fronts of your heels and the backs of the balls of the feet. I often will practice with my toes curled up in my shoes to feel this.
Good knee flex is important, as your legs should work like shock absorbers using the ground for leverage. You should feel some tension in your quads and in the back of your calves to give you a good foundation for your swing.
Your back should be straight and your chin up to keep the spine in line from your tailbone to the top of your head. Feeling like your tailbone is up in the air a little bit is better than having your hips too far underneath you. You should be taller with your longer clubs and more over the ball with the shorter clubs.
Your spine angle also needs to tilt away from the target on the longer clubs positioning your head more behind the ball and be more vertical on the shorter clubs positioning your head more over the ball.