Rolling Hands

         This is a common mistake and one that feels OK as you are doing it. As the backswing progresses the club gets too far inside and behind you and the clubface is open, facing the sky. To finish the backswing you will lift the arms and put the club in a steep and weak position, maybe even getting it across the line.

        If this is your mistake, you need to monitor how much the left wrist rotates early in the swing. Take the club back to waist high and allow only 90 degrees of rotation, so the back of your left wrist is parallel to your body line and the shaft is in line with your toes. The toe of the club should be almost vertical.
 

Disconnecting Arms

         Many players begin the swing by pushing the hands out toward the ball and moving the left arm away from the body. As the handle moves out the club head moves inward, getting it inside and behind. The rest of the backswing is similar to the previous move.

        The fix here is to keep your left arm connected to your left chest and moving across as the swing progresses. Visualize your hands tracking back with your body rotation, rather than moving out.
 

Picking the Club Up

        If all you use to begin the takeaway are hands and arms, you will surely pick it up and chop it back down. The golf swing is a synchronized blend of club, hands, arms, and body movements, and they need to start together. If you are a picker, make sure the core begins to rotate as the club is put in motion by your hands and arms.

Club Head Starts Outside

        The opposite of rolling the hands, this is often the result of trying for maximum extension or an overdone one-piece takeaway. Once your club is outside and above the plane, it must loop back under to get back on plane.