Stand with your feet shoulder-width apart and hold the barbell behind you with your palms away from you. Depending on how heavy the barbell is, you may also have to lean forward a little bit to counteract the weight of the barbell pulling you backwards. This is your starting position.
Lift/curl the barbell up with your wrists as high as the natural range of motion in your wrists allows. Once at the top of the movement, curl the bar back down to the original starting position. Finally, repeat this entire movement for the desired or prescribed number of repetitions.
Perform this exercise in a smooth and fluid motion
Don't allow the barbell to jerk your wrists down too fast as this may result in injury; always be in complete control of the weight
SPECIAL NOTES & LEVEL of DIFFICULTY VARIATIONS
To increase the level of difficulty, slow down the movement or increase the weight.
This exercise is an all-time classic for building forearm muscles. It's good for both beginners and advanced lifters.
The key thing to point out is the balancing aspect of this movement. Namely, if you do this exercise with a heavy barbell you will need to lean forward to counter-balance the backward pulling force of the barbell. Thus, take a moment and find that sweet spot that will give you perfect balance.
Another item worth mentioning is that this exercise is one of the most effective forearm exercises for building bulging muscles in your forearms. You will find that your forearms and wrists will get stronger fairly quick with this exercise. Thus, to keep your forearm muscles challenged you will need to increase the weight regularly and also throw a few other forearm exercise into your forearm workout mix.