A trout thrives in clean, cold water. Running off the tops of mountains or through underground springs, the water of the Shenandoah Valley is some of the finest throughout Virginia. The collection of these watersheds result in trout streams with clear running water with smooth, long pools. Of course this provides for good habitat, however, this puts us in the disadvantage of having to approach these waters where we are easily visible.
Trout are a wary fish, and reasonably so. One reasonably sized stream I fish is constantly under threat from Blue Heron, Bald Eagles, Otters, Raccoons, and Bears. Fish are looking in all directions for these threats, and if they feel uncomfortable at all, then they won't eat our flies. Knowing that if we spook fish, we basically ruin our chances to catch those fish, then it is imperative that we understand how to approach the water and what fish can see.
The first thing to understand is that trout always face into the current, not always upstream, but always into the current. That means if there is a back eddy, that fish could be facing anywhere in 360 degrees depending on the current and where it is located. Trout normally do not swim around and chase food. They actually exist in a 3'x2' area that is their individual spot. They have positioned and fought for that spot in a feeding lane and they do not want to move. They then let food come to them as a conveyor belt as they maintain their position. If anything comes along that makes them feel uneasy: a shadow, stomping in the stream, or even another fish moving around them, then they basically become cautious and hide with the rest of the fish or under a rock or log nearby that provides cover.
Now all we have to do is determine how to approach a stream with this knowledge. From about ten yards or so stay back from the bank. This is the perfect opportunity to get rigged up and see if you notice any rises or hatches around the stream. Look at the current and any side pockets that fish might sit in an eddy or unusual spot. These are the first fish to blow your cover as they'll dart to the deeper water. Second, understand that trout can see back behind their "ears" if they had them. They can basically look over their shoulders, but not above and behind their heads. So we need to approach from the bottom of the pool and cast upstream so the fish only see the fly, not us. While fly fishing slowly move up the bank to not raise any attention to yourself. Slow, methodical casts should be made as the more you cast, the more you make your presence known.Very small streams it is actually helpful to kneel or crouch low if possible. No need to crawl along the ground, but again you aren't trying to present a large object over the water.
Clothing is also something you can take into account. Fish can see color outside of the water, so bright clothing that doesn't mimic nature definitely stands out. No need for camo or face paint, but natural colors like browns, greys, and greens do not stand out the same as neon orange. Even something as small as your hat will stand out as that is the most likely thing that a fish will see first.
Think paranoid like a fish, go slow, and blend in and you'll find yourself spotting fish instead of spooking them.