When looking for the right pair of sunglasses for your face, you want to consider the shape of your face, your skin color, and your hair style. These three factors will determine which style of sunglasses will best suit you. By knowing what to look for, you'll be able to know which sunglasses to try on while at the store. Those sunglasses that best fit and suit your face will complement you and accent your best features.

Face Structure
Oval Face
For the most part, any style and shape sunglasses will do. The best choices will generally be wraparounds or square shaped frames with a gently rounded edge and higher temple. You can pretty much experiment with whatever frame shape or thickness that you want.
Frame suggestions : Any frame shape

Round Face
You want a frame that will make your face appear longer and thinner. You want to look for frames that are equal to or slightly wider than the broadest part of your face. You want to minimize the curves and add definition with a soft, angled, or rectangular style. Sunglasses with a higher temple will create a longer profile, and those with brow bars will pull the eye upward, making the face appear longer. You should also look for sunglasses with a thick frame.
Frame suggestions : Wider frames with angular / rectangular styles

Diamond Shape Face
You'll want to find oval sunglasses that will soften the contour of your face, but at the same time softly curved square frames. Make sure that the style is no wider than the top of your cheekbones.
Frame suggestions : Oval, Square, Rimless

Square Face
You want to choose a pair of sunglasses that will soften your face, as you have a strong jawline and broad forehead. Choose sunglasses that have a soft, curvy frame that will give your face some definition. Oval and round frames typically work well, as do cat eye frames. It's also a good idea to stick with thinner frames.
Frame suggestions : Oval, Round, Cat Eyes

Oblong Face
You want to make your face look wider and shorter than it is, so you want to stick with sunglasses that do not extend beyond the widest part of your face. Stick with round or square frames and frames that have a short, horizontal and a long, vertical line. Also consider frames that are decorated around the temples (studs and jewels are popular), which will add width to the face.
Frame suggestions : Round, Square

Triangle Shaped Face
Because you have a narrow jaw and a wide forehead, it's a good idea to soften the lower portion of your face by accenting your eyes. Frames that angle outward at the top corner and are wide to balance the jawline are great choices. It's a good idea to consider sunglasses that have a metal frame or are rimless on the bottom portion of the sunglasses.
Frame suggestions : Frames with a Straight Top Line, Cat Eyes

Skin
Pale complexions
Consider lightweight frames or those that have a hint of rose or amber coloring. Light colored tortoiseshell sunglasses are also a good option. Stay away from clear, blue, or green tinted frames, as they will drain color from your cheeks.

Dark complexions
If you have an olive, Mediterranean, golden, or Asian skin, you'll find that silver, gold, or clear frames will be perfect for you. Stay away from darker frames.

Dark/Black complexions
If you have a darker skin tone, you'll want to consider a metallic frame. Be weary of black framed sunglasses, as they can either be a horrid mess or a gorgeous sight.

Hair
Soft & curly
Rimless frames and frames with translucent colors will be a great place to start looking.

Very curly
Classic, small frames are going to be the best bet, as will frames that will follow your hairline.

Short
Rounder frames and geometric frames will look the best with short hair.

Very short
Stick with bold colors and designs. Decorative frames are also a good choice.

Long hair
You'll want to consider frames that will benefit you while your hair is down, as well as up, because the change in your hair style will vary the way a pair of sunglasses will look on your face.

Just remember that when you're choosing a pair of sunglasses that you also check to make sure that they offer UVA and UVB protection. A nice polarized lens will help reduce glare. Photochromic lenses reduce glare and help maintain clarity. Polycarbonate lenses offer protection from impact injuries that may be sustained during physical activities. Mirror-coated lenses help block visible light, but not necessarily UV. Blue-blocking lenses block blue light and are thought to make distant objects easier to see, especially in low lighting.

You also want to consider tinted lenses.

Remember that just because the lenses are dark, it doesn't necessarily mean that they will provide better protection.