Accessories for both men and women can break up broad shoulders, creating two shorter shoulder segments rather than one long horizontal line above your chest.
Both men and women can wear a scarf draped down the center of the chest, which breaks up the horizontal line of your shoulders.
Women can add a long beaded necklace to achieve a similar look. Likewise, vertical embellishments around the chest, such as beading along the V-neck of a top, can create visual interest beyond your shoulders.
The structure of a collared shirt serves to break up the line of your shoulders. The collar shortens the distance between your neck and shoulder, creating the illusion of narrower shoulders.