Apart from all the basics, you just have to get out to the range. Today was the monthly CMP sponsored Garand Match at our club. The Civilian Marksmanship Program was created by Congress in 1903. It's purpose was to train civilians to be marksmen. It has gone through some changes, but it still sells rifles and ammunition, establishes the rules for competition, and provides training.
I was shooting a 1903-A3, there were also M1-As, Garands, and AR-15s in today's match. In a Garand Match, it's the historical U.S. military rifles in .30 caliber that qualify for score. We allow anyone to participate, setting aside the scores from other types of firearms.
It's 30 rounds for score. 10 prone slow-fire, 10 prone rapid fire, and 10 rounds off-hand (standing). Possible score of 300 (HA!). To score 300, every round would have to hit a 3 inch circle at 100 yards. The off-hand string is what usually separates the scores. Standing, no sling, iron sights, with a long, heavy rifle. The front sight dances around the target as you try to stabilize things and make a firing decision, then get a 7 to 8 pound trigger to let off while you're still somewhere near the bull.
There's no secrets. It just requires practice. I shot a 267.
I also got to spend a sunny morning with some friends and enjoy the experience of shooting a match with a piece of American history.