First, understand I don't shoot my M1A with a bi-pod, bags, 'n such. I use a sling. I get close to where I think is my natural point of aim, close my eyes, get a good relaxed position and open them if I'm not lined up I adjust.............pivot on the belt buckle. When I'm set dry fire a bit, if I move then it means my position is screwed. If I get to where I can drop the hammer with out moving off my NPA, then I close my eyes, dry fire, open them, and see if any adjustment is needed.
Ride the trigger, meaning don't let the trigger reset until after your follow through and your ready to work the action for the next snap.
If your sights move after you shoot, it means you position is out of whack, means you are muscling the rifle, it moves after the hammer falls because you relax. You should be relaxed when the hammer falls.
Relaxation is one of the most under appreciated parts of marksmanship fundamentals.
If you shoot from a bi-pod or something else, then I'd recommend getting the Rifle's Only DVD and go by his recommendations.
Regardless, when you dry fire, get a note book, data book, score book, something, to record your calls,...............even in dry firing.
Edit to add another point.
Get into a good position with a good solid NPA and get some one to rack the bolt while you dry fire (simulating the firing of the gas gun). Do it with your eyes closed, after the hammer falls, before you let the trigger re-set, open your eyes, if you're not still on target, adjust until you can remain on target.
And yes, the more dry firing the better.