A typical triangular face has a broad forehead and wide cheekbones that narrow to a small chin. To minimize the width of the top of the face, look out for frames that are wider at the bottom, in very light colors or all in one color, and made of light material. Rimless frame styles also help, so check out small square or rounded frames to get a more balanced proportion for the face.
As for a base-down triangular face that features a narrow forehead that widens at the cheek and chin areas, the best way to add width to the top is to emphasize the upper third of the face. Go for frames that play intensely with colors and detailing on the top half or try cat eye shapes.