So many players get out of position in the backswing, usually either by taking the club too far outside or by rolling it back on the inside. What happens is that the rest of the swing is just a recovery from a bad position.
A very simple way of taking the club back on plane is what is called “active arm, passive shaft.” You put your shaft duct-taped to your right arm or looking like an arm-lock putter, and you move your arm back on the perfect plane instead of an active shaft and a passive arm, which gets the club out of position.
From there, the rest of the swing flows through that position so that you can hit compressed, straight golf shots.