I also suggest utoob USMC Fundamentals of Rifle Marksmanship - good stuff to get you going with the basics. Free.
"Position Rifle Shooting" by Bill Pullum and Frank Hanenkrat
... a detailed analysis of rifle-shooting psychology and technique. You might find it or something similar on Amazon.com.
Ex - Navy, Persian Gulf Veteran. Loved shooting the M14, 1911, M60, M2