You have asked a great question.
Actually,the old NRA youth small bore that JFK supported so well is a great approach to prone,sitting,kneeling and standing.The position shooting is where to learn marksmanship.
As far as how to steady the rifle,might be backwards.It will hold still if you let it.
There was a tread a while back on shooting offhand.If you acheive a natural stance where your rifle wants to be pointed at the target (natural point of aim)and your bones are lined up to support your weight,and you have your head erect,so you do not tilt the gyros in your inner ears,you can get pretty steady.Then,you learn to only press on the trigger when the sights are getting closer....
In the field,about 3 handfuls of rice in a plastic bag,put inside a GI green cushionsole sock and knotted up to make a small "ricebag" is light,handy,and you can eat it.Put it on a rock,log,fencepost.etc
Learn to use your gear.I have a ruck I can place in my lap and rest on sitting.If I swing my 2 qt canteen over my thigh sitting,my elbow rests well on it.Prone over the pack,etc.Use what you have.
Often,getting above vegetation is a trick,prone does not always work.
At the final moment,the crosshairs are holding steady enough on target,you KNOW the shot will hit.No poke and hope.Get steadier or get closer,and likely you will have no regrets.