Use a preacher curl bench and an EZ curl bar or dumbbells. Sit on the bench, with your chest against the pad and arms resting on the sloped section. Hold the bar or dumbbells with an underhand grip, hands shoulder-width apart. Curl the weight up towards your face, contracting your biceps. Slowly lower the weight back down to the starting position. Keep your upper arms against the pad throughout the exercise and avoid bouncing or swinging the weight.