Stand up straight with a dumbbell in each hand and an overhand grip.
With the dumbbells in your hands, use your forearms to pull your wrists back as much as you can. You should feel this along the top of your forearms.
Once you curl your wrists upward as much as you can, reverse the motion to slowly bring your wrists back to a neutral position, or slightly curl them to increase the range of motion when you go to extend them.
Seated
Grab two dumbbells (or do one arm at a time with one dumbbell) with an overhand grip and take a seat.
Place your forearms on top of your thighs. Palms are facing down towards the ground.
With your forearms on your thighs, pull your wrists back as much as you can using your forearms, then reverse the motion and slowly lower your wrists back to the starting position.