Alternating, hammer curls. Stand up, with your legs slightly bent, to offer the weight of the dumbbells onto your legs, and so is not to overload your spine. Keep your back straight. Keep your arms next to your sides, gripping the dumbbells in a neutral position. Flex your forearm, keeping your elbow as still as possible. Lower your forearm slowly back to the starting position, and repeat the action with the other arm. Common mistakes. 1. Cheating by arching your back backwards, to facilitate the start of the action. 2. Moving your elbow forwards, during flexion.