Bicep curls tone and develop muscle on the front of the arms. To do standard curls, hold a dumbbell in each hand and rest your arms by your sides. Turn your palms forward and tighten your stomach muscles. Press your upper arms against your sides, then lift the weights slowly toward your shoulders. Stop before your hands touch your shoulders, then lower the weights. Complete 12 to 15 reps, stopping when your biceps fatigue. To do hammer curls, turn your palms inward instead of forward.