If you have long and black, brown or chestnut colored hair, you can try a pair of big black sunglasses. That will make you very cool. In addition, you have a fine and white skin, you can also try big red framed sunglasses that make your more attracting. Or if you have a blond or other light colored hair, you can try some sliver framed sunglasses or purple, grey and brown sunglasses.
I guess the long hair will not be a reference condition for choose the sunglasses. Maybe you should pay more attention on face shape when you plan to buy sunglasses. Usually, people wear long hair should not consider the small sunglasses, because they are not harmonious with the long hair. Try to choose little big frame sunglasses. They will make you better matching with your long hair. Besides, I want to give another advice. You need consider your hair color for choosing the color of sunglasses.
Actually, the length of the hair doesn't affect you to choose shades, but the color and design or your hair makes sense of it. Specifically, if you hair is bright colored with very exaggerating or trendy type, you'd better select some exaggerating styled sunglasses to match your hair style; while if you hair is normal style and normal color, fortunately, you can choose what you like, you do have a big selection of any types of shades.