Shift your weight
To gain more distance, make sure to rotate your body's core, or midsection, through the shot, so your weight finishes on your left side. You want your thighs to finish close together--you should be able to hold a sheet of paper between them--and your lower legs to form a small, inverted V from the knees down (right image). If the V is larger or there's a gap between your knees, your weight is not on your left side (left image). Most likely, you're hanging back on your right foot, which causes the club to bottom out early and hit the ball fat or thin. Reduce the size of the V, and you'll improve your balance and gain distance.
--Cheryl Anderson, one of Golf Digest's 50 Best Women Teachers in America