It might not be the most exciting element of the golf swing, but without a solid, consistent setup position your chances of making a good swing are extremely low. To ensure your body is set properly, focus on placing the majority of your weight in the balls of your feet, with your knees comfortably flexed. From a down-the-line view (as seen here), you should be able to draw a relatively straight line from the knees to the balls of the feet and the butt to the back of the heels. The clubshaft should be pointed at your belt buckle to help promote an on-plane swing. The important thing is to start your swing in a good position, and then maintain it to the finish.
Without a consistent, correct setup position, you have almost no chance of executing good golf shots, period.