Select the appropriate dumbbell weight matching your type of training. Stand in a shoulder-width position with your feet pointing forward. Grab the dumbbells with the palms of your hands facing your torso (inward) during the entire motion. Keep your torso upright.
Flex your elbows and curl the weight upward towards your shoulders without rotating the wrists. The elbows should be close to the torso. Go back to the starting position in the same way. Breathe properly through the whole exercise. Inhale in the starting position and exhale every time you flex your elbow as you go up.
Select the appropriate weight matching your condition, type of training and your fitness level. Start with lighter weight to master the technique well. Maintain your shoulders, knees and feet in a parallel position. Focus on abdominal breathing. Keep your torso upright and make sure you avoid straining your lower back by bending or arching it. Lock your elbows in one position.
Choose an appropriate number of repetitions. Eliminate bending backwards by reducing the weight or by leaning against a wall. Watch yourself in the mirror to maintain the correct stance in all stages of your motion. Watch yourself in the mirror to eliminate using your trapezius muscles. Repeat the exercise with a frequency matching your breathing cycle and make sure to maintain the correct technique.
Hammer curls are curls in which the palms are facing each other. This is the most natural position of our hands thus causing least wrist problems.
Another advantage of hammer curls is that they build brachioradialis muscle that gives the appearance of volume to the forearm.
Hammer curls are usually done with two dumbbells, there is also a special barbell designed for hammer curls (unfortunately not available in every gym).