I can think of four main things you should protect your eyes from:
Sunglasses are the obvious solution. In particular, wrap-around style sunglasses which conform closely to your head will protect the best. Also, you want the lenses to be made of a shatter-proof material, in case you ever crash.
What if you leave home in daylight but don't return until it's too dark to use sunglasses? You could carry a pair of safety glasses with clear lenses, and switch to using them. A nice alternative is to use sunglasses with photochromic lenses. A photochromic lens darkens in response to ultraviolet radiation (in sunlight); the lens will be clearer otherwise (at dawn or dusk, and indoors).
Before buying protective glasses, look through them at any straight-edges you can find, to make sure the lenses are not warped. Warping can cause eyestrain or at least be annoying. You can check for this by both wearing the glasses and holding them in front of you.
Not all sunglasses are equally capable of stopping UV. There are several ways to figure out how good a pair is: