One of the worst faults in golf is not getting off your left foot on the backswing. An equally bad fault is getting too far off it. I find the best way to avoid either fault is to leave about 25% of your weight on the inside ball of your left foot on the backswing, with the left heel just slightly off the ground. By concentrating on leaving a quarter of your weight on your left side, you do two services to your swing: you insure that you get down solid on your left heel on the downswing; you insure that you don't take too much pivot.
Overpivoting is caused by the player's thinking that if he really turns his back on the ball on the backswing, he will "wheel into it" on the downswing. And this is exactly what he will do. He will twist so far away from the line of flight on the backswing that he will be obliged to twist equally far away from it on the downswing. An accurate hit becomes impossible.
As the diagram below illustrates, the player who overpivots and who pulls all of his weight off the left foot not only ends up by doing an off-balance toe dance but the path of his club describes an arc which has a distorted relationship to the true line of flight.
from JIMMY HINES, Thunderbird Country Club, Palm Springs, Calif.