Rest your arm on a table with the palm facing downwards.
Use the opposite hand to roll the ball around the muscles on the top of the forearm.
If you find any tender spots ease into it gently and don't forget to breathe and relax your neck and shoulders. You can also move your wrist up and down or side to side.
To apply more pressure, place the ball on the table and rest your forearm on the ball with your palm facing upwards.
Use your opposite hand to support the arm and guide the forearm on the ball.
Roll around to see what you can find. If you find an area that is tender or is a little restricted, stay on that area and move the wrist up and down. The more you lean over your arm, the more pressure you will apply.
Find a couple of different 'spots' to work on. Massaging these areas little and often is usually best.