Golfers with strong forearms have an advantage on the course. A strong grip allows you to hold the club firmly while keeping your muscles relaxed; this increases your potential distance (relaxed wrists create more club head speed) and improves your shots from the rough. There are a variety of exercises you can do, and you do not need expensive equipment to do them--some require no equipment at all.
Dumbbell Wrist Curls
You can do wrist curls using light dumbbells or any small weight, such as food cans from the grocery store. Do them in various positions--palms-up, palms-down or hammer grips (holding the weights vertically rather than horizontally, which mimics the cocking action). You can do them with one arm at a time or both, and you can do them while seated (with your elbows resting on your legs) or standing, either with your elbows resting on a bench or just hanging by your side.
Barbell Wrist Curls
Barbell curls are not as versatile as dumbbell curls and require more room because of the size of the barbell, but you can do many of the same exercises as you can with dumbbells.
Self-Resistance Wrist Curls
For this single arm wrist curl, you provide your own resistance. Sit in a chair and rest one elbow on your leg, curling the fingers on that hand into a fist. Place your other hand on top of that fist and press down, using your open hand to resist your efforts to curl the fist wrist. Repeat the exercise, reversing each arm's role. Not only does this exercise require no equipment, but you have complete control over how much resistance you provide.
Take an open sheet of newspaper in one hand and try to crunch it into a ball using only that hand. This exercise strengthens the finger muscles as well as the wrists.
Wet Towel Twists
Try to wring all the moisture out of a wet towel. Do it with both hands palms-up, then both hands palms-down, then with one hand up, one hand down and finally with one hand down, one hand up. This exercise works your forearms through a range of up-and-down motions.
Lock and Pull
Interlace the fingers on both hands, then use your arms to try and pull them apart while resisting with your finger strength. This exercise is surprisingly effective; do not pull too hard when first starting.
The Atlas Approach
Charles Atlas was well-known for his “Dynamic Tension” exercises, which involved simply tensing muscles while moving them through a range of motion. This is perhaps the easiest way to give your forearms and fingers a good workout since you can easily create workouts that duplicate the golf swing, even if you do not have room to swing a club. Be aware that you need not tense your muscles anywhere near maximum effort--a little tension goes a long way.