The wrist curl is a basic exercise for the forearm. Using a dumbbell for a single-arm exercise, or a barbell to exercise both arms at the same time, rest the arms palm up on a flat surface and slowly curl the weights toward your biceps and back down while keeping the arms stationary. This works the inside of the forearm. You can also do this exercise on a cable machine: Sit and hold the handles of the cable, palms up with your arms resting on your legs. Once ready, curl the wrists toward you.
With palms face down at your sides, hold two free weights or a barbell. Then bend your elbows and lift the forearms up toward you to work the front side of your forearms. If you think about your golf swing, when holding your club, one of your arms is pushing the club, while the other arm is pulling the club. Therefore, both sides of the forearm must be strengthened.
Sit and place the arm on a surface about armpit level, bent at the elbow and horizontal to the floor. Using a small dumbbell weighted on only one side, hold the dumbbell so it is vertical to the floor with the weight at the bottom. Hold the dumbbell so the thumb is near the top. Now rotate the hand toward your body about 90 degrees so your fist moves horizontally and so does the weight. Rotate to both the left and right in order to strengthen the forearms.