Standing sideways against a wall with arm straight and out in front at about 30°. Press the back of the wrist into the wall as if trying to push the wall away.
Press at a comfortable resistance (~20% resistance to start). Make sure your arm does not move and that you relax your head and shoulders.
Hold for 10-20 seconds.
Release and repeat 2-4 times on each side.
Repeat 2-4 times a day especially before activity and after periods of inactivity.