Your knees should be slightly flexed and directly over the balls of your feet for balance. The center of the upper spine (between your shoulder blades), knees and balls of the feet should be stacked when viewed from behind the ball on the target line. Also, the back knee should be cocked slightly inward towards the target. This will help you brace yourself on this leg during the backswing, thus preventing lower body sway.
Your body should bend at the hips, not in the waist (your buttocks will protrude slightly when you are in this correct posture). The spine is the axis of rotation for the swing, so it should be bent towards the ball from the hips at approximately a 90-degree angle to the shaft of the club. This right angle relationship between the spine and the shaft will help you swing the club, arms and body as a team on the correct plane.
Your vertebrae should be in a straight line with no bending in the middle of the spine. If your spine is in a "slouch" posture, every degree of bend decreases your shoulder turn by 1.5 degrees. Your ability to turn the shoulders on the back swing equals your power potential, so keep your spine in line for longer drives and more consistent ball striking.
When viewed from face on, your spine should tilt to the side, slightly away from the target. The target side hip and shoulder should be slightly higher than the back hip and shoulder. The entire pelvis should be set an inch or two toward the target. This places the hips in the lead and it counter balances your body as your upper spine leans away from the target.
Your chin should be up, out of your chest to encourage a better shoulder turn. The head should be tipped at the same angle as the spine and your eyes should focus on the inside portion of the back of the ball.