Whether you’re in Chile or Montana, when dry fly fishing from shore or wading, the best approach, if possible, is to start in the ‘tailout’ and work your way up the pool. Fish are almost always facing into the current, up stream, so by fishing from the tail of the run to the top, you are in the fish’s blind spot and you can better sneak up on the fish.
Another reason to fish from below is that it’s easier to get a better drift – your fly will float more realistically, the same speed as the current.
Cast from below or to the side of your targets, trying not to line the fish – meaning “don’t cast the fly or line on top of the fish”. This will spook the fish.
Lay the fly far enough ahead of the target so you can get a mend in the line if necessary, setting up the fly so when it gets in front of the fish, the fly floats naturally.
When fishing really small dries, it may be hard to see the fly and if there is glare on the water it may be impossible. Keep your eye in the general area of where you think your fly lands and follow that area down in the current looking for a rise.
One thing to keep in mind – the slower the water, the more time the fish has to look at the fly. Educated fish will often reject an almost perfect imitation so sometimes a small dry is better. If fishing a big dry in slow water, a good trick is to “twitch” or “skate” the fly to make it seem alive. This can make all the difference.
Yet another reason to start from below and work up – when you hook the fish, they usually run downstream and you won’t disrupt the rest of the pool.