How to properly perform dumbbell chest flys for maximum effectiveness?

To perform dumbbell chest flys effectively, lie on a flat bench with a dumbbell in each hand. Start with arms extended above chest, palms facing each other. Lower arms out to the sides in a wide arc, keeping a slight bend in elbows. Stop when arms are parallel to the ground, then bring them back up to starting position. Focus on squeezing chest muscles throughout the movement for maximum effectiveness.