Sight picture!!!!!
Your mind and your body must work together so that the BREAK occurs when you see the proper sight picture.
To achieve this I :
1) Work on upper body strength and cardio, including hoisting a heavy rifle into position over and over in dry-fire, as I breathe, hold, tension trigger and BREAK. Over and over and over. SEE the shot.
2) Use lots of .22 to practice.
3) Tension your muscles evenly and only as much as needed.
4) Practice with a 'real' gun too.
5) Use anything that works for you....sling, elbow positions, weight on legs, etc....
6) Don't over-correct your sight picture. If you do your wobble will INCREASE. Ease into the shot and relax. I try to come up to the aim and NOT push past the target and have to bring it back again....ie all one smooth motion.
7) By the time I'm ready for the shot in the aim position, the trigger is already pre-tensioned so that finding the trigger doesn't create a 'jerk' in the system. I'm already there. I don't bring it up, aim, hold breath and THEN fiddle around to find the trigger. Again, all one smooth motion (However, I'm NOT on the trigger until gun is on target.)
8) Being able to see the shot BEFORE you bring the gun up, and then bring the gun up into position saves time. It's like a pistol, or ironsights....your eye is on target, the gun (and sights) comes into alignment with your eye, you pause, and squeeze. You only have a few seconds before your muscles tire and you must breathe, so this is the efficient way to do it.
9) Get a good shoulder pocket and cheek weld. Practice holding the gun in the same spot each time. I put the butt in the open shoulder pocket by raising my trigger-hand elbow. It anchors on my collar bone. This stabilizes my pulse and is very repeatable.
10) If you flinch, you need to retrain to let the shot happen and just pull the trigger. Everything else happens on auto-pilot after that. Dry fire and .22 is good for retraining if needed. Repeatability (ie 'shot goes where I want it.') hinges on stability at the time the trigger breaks.
11) Finally, as I'm raising the rifle, I'm breathing in. By the time the rifle is up, my breathe is paused, my body is stabilized, the trigger is pretensioned, I see the sight picture, my arms are in position and my cheek is in contact. All that is left is a slow, steady squeeze. The shot happens when it happens, but if I've done my job right up to that point, the break coincides with my mental sight picture brought from lots of practice. It becomes reflexive.
Sorry for the long winded reply.
I shoot Service Rifle to good effect in Standing Position with the above tips, including running from the 500M line to eventually make it to the 100M line and shoot 3-second target exposures, with an AR15 (which according to the Antis is not used for competitions....)
I train with a heavy rifle in dry-fire to make the AR feel ..... lighter.
For hunting the only thing left is to learn how to make use of supports like trees etc without have the recoil rip the skin off your knuckles on the bark!!