Design the machine so that operating components can be manipulated with the wrist in a straight position.
When precision is the requirement, choose components with grips in the 1/4" to 1/2" range. The smaller diameter prevents overexertion of fingers, knuckle joints, and hand muscles.
For operations that require force, look for components whose grips have handle or knob diameters that range from 1 1/4" to 2." This allows for fingers to wrap comfortably in a firm hold.
The 6830-NI toggle clamp on the right has excellent ergonomic features such as these.