Did you know the golf swing has two centers, an upper, and a lower?
The approximate location of you upper center is the top button on your golf shirt (if you have it buttoned). The approximate location of your lower center is your belt buckle.
Controlling both of your centers will lead to better contact every time. I use two good drills to check for proper positions of these two points before and during my student's swings.
Prior to hitting a ball, your two centers will be vertically in-line with themselves. To experience this alignment, grab a club and a golf ball, and put yourself your normal setup position. In this position, you should notice that your two centers are in a straight vertical line. If they are not, then your set-up position is out of balance, and you should make a correction to this position to insure the two centers form a straight line. A good drill to practice is setting up in front of a mirror, visually checking to see if your two centers are in line. Drawing a line down the middle of the mirror will assist you in achieving the correct position.
When you are in an impact position in your swing, your centers are no longer in line. Your lower center must be ahead of the ball, on its way to facing your intended target. You upper center should be in line and/or behind the ball. If they are not in these positions, chances are you are making a reverse weight shift. A good drill to achieve this desirable position is to again use a mirror. This time, try to insure that as you swing the club down, your lower center passes the line you have drawn on the mirror, while your upper center remains behind the line.