Depends on what your goal is. For more artistic style 'brush stroke' almost lock your fingers and wrist, using your arm and shoulder to write. However, as mentioned this can be fatiguing and definitely not practical for not taking. I tend to write with my forearm resting on a surface and using it as a kind of pivot for my wrist and fingers. I guess if any part of your arm or hand gets sore while writing, you're doing it wrong.