It pays to acquire a clear mental picture of at least one of the two tracks of the swing. One of these two tracks is that of the clubhead, the other the track of the hands. Many people find it easier to keep track of the hands.
The swing is sometimes spoken of as being circular. It is not. It is more egg-shaped. The arc is nearly a circle at the top of the backswing and the top of the forward swing, but it is definitely flattened from waist-high to waist-high.
One reason for this is that the left arm is straight through the backswing while the right arm bends; and the right arm is straight on the forward swing while the left arm bends.
So the track of the hands going back is backwards and inwards on a slight curve until nature swings them up.
On the throughswing the hands come down, then swing again in a slight curve from beside the right hip to beside the left hip. They aim toward and ''through'' the ball, but never of course beyond it.
One can practice ''keeping track'' at odd moments and at any time without a club. And keeping the track in mind when playing will help enormously.