Start your backswing by turning your shoulders to the right (for right handed golfers). Your shoulders and upper body should rotate over your lower body so during the first part of the backswing your lower body is very static.
Once your shoulders have achieved a 45 degree rotation to the right, your hips will now begin to rotate for the final part of your backswing. You are looking to achieve a 90 degree rotation to the right with your upper body and only a 45 degree rotation to the right with your lower body. This will allow you to create a great deal of coil or twist within your torso and it is this coil that gives you a compact feeling.
If you allow your hips to over rotate beyond 45 degrees this will allow your shoulders to rotate more and you will lose the compact feeling in your backswing. The over rotation will produce a longer backswing but less coil and as such your swing will produce less power as you will not spring out of your backswing.
In order to create a compact golf swing, rotate your shoulders to 90 degrees but keep your hip rotation to only 45 degrees.