When using a lap board make sure at least half the lap board is below the contact point where it rests against the table. The angle between the lap board and the plane made by your thighs shouldbe at a minimum of 45 degrees and the light source should be on the opposite side of your drawing hand and positions in such a way that the reflected light hits you in the belly. This is to avoid glare on the working areas and to control any shadows made by your drawing hand by projecting them away from the working area.
Carpal Tunnel Concerns
Your wrist should never be flexed in an upright manner while you are working. It should either be in line with the forearm or slightly bent inward to avoid the tension which causes carpal tunnel syndrome.
Lock your wrist and make the strokes with your elbow or shoulder
with your back and neck straight. Never hunch over your work.