For more than 40 years, Lefty Kreh has flyfished around the world for a wide variety of freshwater and saltwater gamefish. When he talks, it pays to listen. The angler who fishes carefully along the stream bank in deep shade is much less likely to be seen by the fish than the angler working in sunlight. Approaching from the shaded side gives you an advantage. This is often obvious when you're fishing streams in the East, but it might seem not to apply to bigger Western rivers.
Most Western riverbanks are fairly light in color, however, as is the brush in many areas.
By approaching from the shaded side you'll reduce the contrast between yourself and the bank, lessening the chances of being seen by the fish. Before making that first cast, always consider how you'll hook the fish, how you'll fight it, and how you'll land it. I've sometimes successfully cast and hooked a big fish in a rush. But when it came to landing it, I was in such a position that I couldn't. No matter how well or how far you can cast, if you don't hit the target, you've missed the opportunity.