When I am doing fine work, like fine painting or tweezer work, I try to keep both hands supported and connected to the same support. Sometimes I will put a box down on the bench top, with my left hand resting on the box and the paint brush or tweezer in the left hand, also resting on the box.
If that is not pratical, or when the model is sitting on benchtop itself, I will place left hand on bench near where I am working on model, making a fist, and have right hand resting on left, or forearm near wrist, resting on the left hand fist.
I try to make all the motion with the right hand and fingers. I never to any fine work with neither right wrist area nor elbow supported by workbench. Sometimes both forearm/wrists resting on work benchtop, model or piece to be worked on in left, tool or brush in right.