Natural Point of Aim is something we often take for granted. We line up straight behind the rifle, which gets us 80% of the way there, and then shooting a heavy rifle in the prone will mask the errors.
Where NPA errors really show up is in Alternate Positions and Sling shooting. Shooting from a Tripod, off a Barricade or other obstacle is where we see NPA errors the most. Once we get off the ground, the body's reaction to the shot will create that relaxation that shifts us off the target. So it's important to not only practice setting up our NPA, but to understand how well we are executing the fundamentals of marksmanship as a whole.
We have this drill, where the shoot adjusts their NPA on the target, then taking the sight picture away, we hesitate and fire. This helps us see if we are drifting off target and which way.
This drill is best accomplished with a second person helping. In the video I close my scope cap, being alone it requires a lot of movement. With a second person there to help you can line up on the target, and have them close the front cap on your scope. Be sure to hesitate before firing. If you immediately shoot you don't have time for the body to subconsciously relax on you.
This subconscious relaxation is what causes us to drift off target.
I am doing this drill in the prone, using a target at 450 yards, but you can do it from any position and it is recommended you do it from alternate positions.
Trigger control is one of the biggest reasons we move off target, and this will also help you diagnose any potential problems with trigger control. You will see which way the shots are going. If you need be, use a bigger target. Put a fine aiming point on it, and then see how far from center the shots drift.