While typing, even if it's just for a short while, you should sit back fully in your chair. Your hips should be all the way back in the seat, and your back and shoulders should be pressed against the upright back of the chair. Your arms shouldn't be fully resting on the desk or keyboard, but sort of "floating" just above them -- this may feel weird at first, but it allows your wrists to maintain a natural arc that's more comfortable in the long term.Also: The best ergonomic office chairs