Frequently, trout refuse to take your dry fly because it is not drifting like a natural fly on the surface of the stream. Simply showing the trout an artificial dry fly which matches the hatch may not be enough to catch him.
This unnatural drift of a dry fly is referred to as DRAG and it is caused by the currents between the trout’s feeding station and the artificial fly pulling on the leader. In order to prevent this problem, I use a slack line east. My favorite is the puddle cast. In order to achieve a puddle cast, I extend 6 to 10 feet more line on my presentation cast than I need to reach the target. As the fly line goes forward on the presentation cast, I stop the forward motion of the fly rod at 45 degrees over the stream. This permits the leader to fall in a puddle, which enables the fly to drift naturally to the trout which usually produces a solid strike.
Another slack line cast which I use is the Lazy S Cast. In this case, as the presentation cast is flowing forward, I wiggle the rod tip back and forth from right to left. This creates curves in the leader and line, so when these settle on the stream, they remove the pull of the leader on the fly and allows the fly to drift naturally just like a reel insect. The trout take my fly solidly.