Choose an appropriate resistance. Grasp a low pulley cable with a supinated grip (palms up). Sit down on a bench with your feet in a shoulder-width position, knees bent (90 degrees), torso upright and pelvis in a neutral position. Bring your arms up so that your forearms are resting against the top of your thighs. Your wrists should be hanging just beyond your knees. Your torso is slightly tilted forward.
Start by curling your wrist upwards while contracting your forearm muscles. As you go to the starting position, bend your wrist down a little bit (dorsal flexion). Repeat the motion as required. As your wrists go up, breathe out and breathe in as you go down.
Make sure you keep your torso straight without overarching your upper back.
As you start, choose an appropriate resistance to master the technique well.