Rest the back of your forearm on a table or on your leg. Your palm should be facing up, and your hand should be aligned with your arm. Place a light weight in that hand, then slowly lower the weight toward the floor. The movement should take you five seconds, then bring the wrist back up to starting position. 
 Do two sets of 10 or 15 reps with each wrist four or five times a week.

Grab a dumbbell, then stand with your arms at your side. Tilt the dumbbell toward the ceiling and slowly lower it down. Do two sets of 10 or 15 reps with each wrist four or five times a week.

Place one hand on the back of the other with the hand flexed towards the wrist. Hold the hand in place by applying some pressure on it and move the forearm lower to increase the angle. Hold for six to ten seconds, then work the opposite arm.

Get on your hands and knees and place your hands flat on the ground with your fingers pointing back toward your body. Keep your arms straight and locked and stretch your wrists gently. Don’t force them. Count to fifteen. When you get comfortable with that stretch, try to extend your legs out behind you and bring your hips down to the ground while pushing your torso up by fully extending your arms with your palms flat on the floor. In yoga, this is called the “cobra pose” and it can be very effective at stretching your wrists.

Grip the bar over hand, with less weight than you’d use for a bicep curl. At the curl station, instead of bringing the bar all the way up as you would in a bicep curl, flex your wrists to bring the bar up. Do the same number of sets and reps you use for bicep curls. Repeat the exercise with an under-hand grip as well.

Line up one or two plates from the weight machine on the ground, perpendicular with the ground. Squat down, gripping them with your hands, then stand up, holding it securely. That’s it. Alternate hands, doing three sets of five-ten reps, or whatever is comfortable for you. You could also use a stack of a few heavy books, something that will stretch out your grip and force you to spread your fingers relatively wide as you lift. It’s mostly about the strength required to grip the objects together.

Grip the bar with both hands, palms facing down and extend your arms straight out in front of you. As the weight hangs, twist the bar up and backward with your wrists, one at a time, as if you were activating the gas on a motorcycle. Try 10 or 15 reps at three sets.

Focus on keeping your wrists very straight and solid while you do push-ups, however many you’re comfortable doing. If you’re just getting started, try doing three sets of ten.