Firstly, we shake and there's no way to completely stop that. Heck even braced on a bench we still move at least a little bit. Given that it amazes me how accurate some of us are in the first place.
Things that have worked to reduce shake for me.
-No caffeine
coffee, soda, tea
-Learn some stretches for the hands and arms
there are such things in yoga and they do help.
-Learn your "pattern".
Between natural movement and breathing I move in a slanted figure eight so once I learned to time things to the "center" of the pattern I got a lot better
-Strengthen your forearms and grip.
I use a
"ProHands" sometimes but mostly I play around with a
Dynaflex "power-ball".