First, make sure the sunglasses you want to buy can block 100% UV rays. Next, choose the right style that go with your own style. If your face is small, then look for smaller glasses. If your face is larger, then look for larger glasses. Remember not to choose the same shape glasses as your face shape. Otherwise it will look ugly on you.
Dark tinted color lenses can protect you from brightness, such as brown/gray/green.Polarized lenses could also prevent you from glare. If you often work outdoors, you'd better choose these kinds of lenses.
According to your certain situation, I'd like to give you some suggestions in choosing a pair of sunglasses. First, you should buy some sunglasses with a good quality. The lens must protect you from the strong UV during the day. Secondly, you'd better choose the bigger ones. Because the bigger the sunglasses are, the more area they will cover on our face. Therefore, we can protect the skin on our face. At last, you can buy the sunglasses in dark colors, for it can help to block more beams of sunlight and make our eyes more comfortable when we are exposing to the sun during the day time.