When choosing glasses for square-shaped faces, the goal should be to lengthen and soften the face's natural angularity and to avoid frames that could exaggerate the sharpness of facial features. By adding curving lines, you can make a square face appear thinner and softer.
Rounded and upswept frames will add curves to the face while drawing attention away from the squareness of the jaw. A good rule of thumb for people with square faces is to choose glasses that are wider than they are deep (i.e. tall), as wider frames give the illusion of a slimmer face. Another trick square faces can try is to select glasses in neutral colors (cream, beige, etc.), which help soften the angles the face. Finally, oversized frames, like Jackie-O exaggerated rounds, help to distract from the harshness of a square jawline.