Clubface aim and swingpath are linked… and often in the form of a vicious circle. As the face opens, the right-handed golfer hits further left to allow for it; and the further left he hits, the more he opens the face.
This relationship causes problems both for the high-handicap club player, who tends to start down with his upper body and attack the ball from the outside; and for the better player who can get over-active in the legs, leaving the club behind and approaching the ball too much from the inside.
The solution to both problems begins with altering face aim. The slicer holds the face open. He needs to train his arms to work earlier in the downswing to square the face via a full and free forearm rotation through the ball; feel the face points to the ground at hip height on the way through.
With the shaft horizontal, pitch the leading edge at a sharper angle than your left arm. A closed face spins the ball left, so you must learn to hit out to the right to keep the ball on target.
In practice start with the club opposite your back toe. This closes your shoulders to the target, giving you the feeling you can attack from the inside and send the ball right of the target.