One of the more common faults I see with many of my students is a lack of arm, hand and wrist action, combined with too much body action. The player lacks a gifted player's natural clubhead speed, and tries to make up for it by copying his body action. This invariably leads to a hectic and unbalanced movement. Rather than swinging the clubhead into the ball they are throwing their body at it.
When this occurs the results are a lot of sliced shots and topping or thining others. The player is using too much body action in the downswing, relative to their arm and hand action. The fault generally begins at the moment the player transfers from the backswing to the downswing. It is caused by uncoiling the body too fast almost violently, in relation to their arm and hand action.
The effect of this excessive unwind of the body is to delay your arm and hand swing so the clubface arrives open at impact, and on so steep a plane that it only hits the upper portion of the ball. The player has hit too late with their arms, wrists, hands and clubhead, and too early with their body.
If you are slicing or topping shots, simply slow down your body unwind and increase the use of the clubhead by increasing the speed of your arm swing. In other words hit earlier with the clubhead and later with your body, until the flight of the ball tells you that your timing is better coordinated.
Visualize the motion of swinging the clubhead down and through the ball with your arms before the shoulders unwind. An excellent drill to capture this feeling is to hit balls using a five or six iron with your feet together. Tee the ball up slightly and swing about eighty percent of your normal speed.
With a little practice you'll be amazed how solidly you'll strike the ball and the distance the ball will go.