If you fidget when you shoot, you will not shoot well. Seriously. You may think that tiny little tapping of your foot on the floor is no big deal- but it can spread out a group badly.
Best practice: do everything you need to do before you start shooting. Gotta go to the bathroom- do it before you take your position. Spotting scope not quite in the right place- fix it now. Ammunition cumbersome to pull from the box- now is the time to adjust that. Does your eye itch, need to wipe sweat away? Do it before you shoot.
After a long, steady session of shooting, your body should be marked with all of the places it contacted the ground. Your legs may go to sleep in standing position, your foot will definitely be asleep if you kneel. You will have marks from your shirt or shooting coat and jeans on your knees, legs and elbows.
Sometime, practice getting into position and staying there for a while without shooting. You can do this in your home. You’ll see how much you fidget when you are looking for it.