Firearms are perfect. They do not move on their own. Guns neither shake nor wobble. Once pointed they will stay on target, at least until a human being gets involved. The shooter is the force that moves the firearm off target. 

Shooters are not perfect. Muscle, nerves, breathing, and circulation are movement. The large moving thing disturbs the small perfectly still thing. Shooters make guns move.

Sadly, none of this can be prevented, but movement can be greatly reduced. To lessen movement, lessen the influence of the body. To lessen the influence of the body, reduce muscular tension, which will  reduce nerve twitching and calm circulation and breathing.

Stop over-gripping, crouching, tightening your muscles and otherwise doing everything counter to your own good sense. What is popular is not necessarily what is right. Stop it. Think it through. Relax.

If your shoulders are not ahead of your hips during firing, you will exaggerate recoil, become imbalanced, and fire with less speed. Here's an easy way to adjust your posture for quick, stable firing: Stand upright and naturally. Slump your shoulders forward so that your hands naturally rest on the front of your thighs. Now lift your arms into your shooting position. (Remember, hands go to the head, not the other way around.) That's it. You don't need to lean far forward, just get your shoulder carriage slightly in front of your hips. Look in the mirror to see the change and commit the feel of the position to memory. Do it every time you shoot.