Eyewear

Getting a suitable frame lies pretty much on the face shape. 7 basic shapes are listed here (bear in mind that some of us have combinations) :

Diamond
Determined by the fact that cheekbones are wider than the brow bone and jaw line, the trick here is to wear frames with oval, soft-curved square, cat-eye or rimless shapes and frame width must not be wider than the top of the cheeks. Try to avoid frames with decorative upper rim.
Heart/Inverted triangle
As the same suggests, this face shape has a broad forehead narrowing towards the mouth area and a pointed chin. Go for smaller, rounded or square designs with emphasis on the lower sides. Avoid frames that are wide at the top or with decorations on the upper rims.
Oblong
With a face length longer than its width coupled with a long straight cheek line, go for frames that are wide, with strong bridges and decorative temples.
Oval
No restrictions, choose any frame that pleases as long as it is not too big or too small for the face.
Round
With a face width more than 2/3 the length and where cheeks are more obvious than cheekbones, an angular frame makes a round face look longer and narrower. Try frames with decorations on the upper rim. Avoid oval or round frames.
Square
To soften the prominent jaw line, broad forehead & an equal-size length and width, opt for a frame that is curved at the side and corner. Square or angular frames are definitely a no-no.
Triangle
Defined by a broad bottom with respect to a narrow forehead, choose a frame that is wide and bold with emphasis on the upper sides so as to draw attention off the lower face. Avoid small frames too. Try cat-eye style.

Plastic - lightweight, less likely to break, wide variety of designs and colors.
Stainless steel - lightweight, durable and will not corrode.
Titanium - lightweight, stronger than stainless steel and hypoallergenic.
Silicon nose pads - give better comfort.

Sunlight consists of 2 types of light waves or radiation; visible and invisible.
Visible light has a spectrum of 7 colors ranging from red to violet.
Invisible ultraviolet (UV) radiation is not possible for detection to the human eye, e.g. infrared and X-rays. UV radiaition is further divided into 3 different types - UVC, UCB and UVA.
The very toxic UVC is filtered out by the ozone layer. The ozone layer also filters UVB but about 1% of UVB still passes through to reach earth. UVB is what causes sunburn and even skin cancers after prolong exposure.
UVA is abundant around us since the ozone layer poses no obstruction. UVA is what causes photoaging of the skin and is linked to photosensitivity resulting from certain diseases (e.g. lupus and the consumption of some drugs and herbs (find out which are the ones here).
Whether the weather is windy, cloudy or foggy during the day, harmful UV rays are still able to penetrate through.

Gradient - 2 shades on these lenses; darker shade at the top and lighter at the bottom.
Photochromic - lens that darken when outdoors & lighten when indoors.
Polarised - lens that cut glare from sunlight reflected from flat/horizontal or other reflective sufaces, e.g. water, highway, & snow.

Select sunglasses that offer protection and not because they are trendy. A good pair should be wrap-around (do not forget light enters from the side), with UV protection and comfortable.
See Face matching frames.
The color of the lens has got nothing to do with UV protection.
Plastic lenses usually blocks out more UV rays than glass lenses.
Lenses should not be darker than an 85% percent tint because that would simply reduce the amount of light getting to the eye which in turn enlarges the pupil and lets more light through.