The best anglers have not only impeccable mechanics, but they also have a supreme ability to read and pick apart productive water.
In fact, I'd say that not thoroughly fishing productive water is one of the most common problems I've noticed over the years. It's great to have a wonderful presentation and to be using a highly-productive fly, but if that fly isn't visiting the very best nooks and crannies where the fish actually want to lay and feed, then that angler's success can be severely dampened.
I've always been very meticulous about dissecting productive water. I guess that just comes with my thought process and the fact that I'm naturally very particular and methodical when it comes to many things. This can be both good and bad on or off the water, but out on the water it lets me often catch fish that others pass by.
One of my favorite places to fish here locally is a large urban lake that's full of nice largemouth. Like most South Florida lakes, it's surrounded by homes but is somewhat unique because it has a bunch of foot bridges going over narrow fingers of the lake. The bridges provide ample shade any time the sun is shining, and fish can often be holding anywhere in that shaded area. However, that general area is not the most consistent "zone" to fish.
While the shade of any of these bridges are often great spots to just cast around and have a shot at getting a grab, there is a definite "spot within a spot" on some of these bridges—the concrete walls supporting each end. When the water is up, fish often hold up tight against the concrete walls right where the concrete meets the bottom, which is typically only about 1–3 feet deep. If the fly doesn't land and sink right up against the wall, often times no bite comes. I can't tell you how many times I've thrown casts that landed just a couple feet short of the wall, then when I finally did smack the fly right up against the wall and let it sink, BOOM, there's the bite.
This is just one of many examples where the fly often needs to be in a very specific place to get bit. I've experienced it with MANY species from small stream rainbows to tarpon.
The strike window of fish can be very small—especially in dirtier water, when they are inactive, or when hunkered down waiting to ambush something that gets close. Rather than only sprinkling casts throughout the general area of a spot you're fishing, focus also on small, key ambush/holding areas that may exist within that spot and make sure to get the fly right into and around those special places. This can be a small bit of shade, the very head of a current break, a tree root....the list is immense.
It might take some casting expertise and you may sacrifice a fly or two trying to hit some of the more difficult spots, but it can be well worth it. Many folks pass by the difficult or less-than-obvious spots, or simply don't fish the fly close enough to even the most obvious fish holding zones. Be a thorough fly angler and fish methodically!