Cowboy: I don't know about WW2 to present, but damn things sure changed from WW1 to WW2.
I have a Small Arms Firing Manual printed in 1918. Got it for $5 in a junk store up in IL. Anyway, they used to recommend pulling the trigger with the inside of the middle knuckle of your index finger. They also told people to concentrate on keeping the target in focus. It's odd to read from a modern perspective.
On the other end of the spectrum: last year I talked to a Marine fresh from boot camp, who told me that they're not teaching shooting with iron sights anymore. I find that very difficult to believe.
As others have said, there's a lot of info out there. Do you have any specific questions related to shooting technique? Positions? Breath Control? Trigger Manipulation? Sling Usage? Sight picture? How to set up a rifle that fits your body? How to practice without sending rounds down range?
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