Balance is the foundation of a good swing. By far the best training exercise I know for building better balance involves using two props—I usually suggest two ordinary glass tumblers, because they're common to every household, though any objects generally resembling them in size can be used. Place these tumblers so that, when you take your stance, one tumbler is just to the right of your right heel and the other is just to the left of the left heel (see the diagrams below). The idea is to accomplish your footwork correctly between the glasses, to hit neither glass as you perform your swing.
This exercise is a wonder for checking and correcting two very common faults: 1) swaying on the backswing and 2) hitting from the outside on the downswing. Swaying is caused by the left heel's turning outward, toward the hole, when you start back. Many golfers don't know when they sway. You can tell when you do when you work with the tumblers, for your left heel will kick over the left tumbler when it turns out. Secondly, if your right heel turns out on the downswing and kicks over the right tumbler, you know for a fact that you're swinging outside the correct line to the ball.
Work to swing so that you touch neither glass. You will prevent hip and shoulder sway. You don't have to think about your hips. They'll turn "inside" the feet.
from HARRY OBITZ Shawnee Inn & CC, Shawnee-on-Delaware, Pa.