Rather than repeat previous posts, I discussed mending for dry flies and indicators in the posts below.
The cast...specifically the last 2 seconds!
How To: Drift an Indicator Nymph Rig
You asked about mends so I posted the above threads. Another way to correct for drag is with a curve cast which occurs before a mend.
A technical point is that casts and mends are related but separate concepts and they have separate definitions.
I use the following definition to separate a cast from a mend. The cast is defined by the motion of the rod tip up to the stop. A mend repositions the line with the motion of the rod tip after the stop either while the line is in the air or on the water. This seems to agree with:
"Difference between a "Mend" and a "Cast" - a Cast is something you make during the Casting Stroke and affects the fly-leg of the loop, while a Mend is something you make after the loop has formed and affects the rod-leg of the loop. And that's all we'll say about that."
Preparing for the FFF CI test
So curve casts are also way to compensate for drag.
In the air mends are rod movements after the stop to reposition the fly line before it lands. The line is repositioned in the air by moving the rod tip after the stop.
Here are the rules of in-the-air mends
1. There are 3 planes (dimensions) in which the rod tip can move after the stop = Right-Left (R-L), Up-Down (U-D), Forward-Backward (F-B)
2. The shorter the delay after the stop, the closer to the fly the repositioning begins.
3. The difference between an-in-the mend
vs a cast is that the rod tip movement occurs after
the stop. For a cast
such as a curve cast, the rod tip movement occurs before
3. Mends can be combined with other mends and
casts to produce different mends.
Obviously the simple single reach mend is the first, and I think you know how to do that. But now test out rule 2 by delaying the reach a bit after the stop and you will see that the fly and leader are straight and the cast deviates to the side of the reach depending on the amount of delay of the reach.
Now try a reach to the right and immediately bring the rod back left to the center. you will see that the fly line goes right then back left, creating a right sided curve. Try changing the timing of the R-L movement to move the curve closer to you or closer to the fly. Try varying how long the rod tip stays to the right to control the length of the curve. Try varying the amount you move to the right to cary the depth of the curve.
By varying the timing, the amount of movement, and the delay in moving back to the left, you can place the curve around a rock to control the side of the rock the fly will fish, or place the curve directly in a current stream to compensate for a section of differential flow.
All of these mends originate from the simple basic reach.
Similarly by directing a cast upward and mending down after the stop, you do what is commonly called a puddle cast but really is a puddle mend. This is good for complex currents where a single directional mend cannot compensate for the multiple currents.
By suddenly mending back immediately after the stop, you shock the line and line and it bounces back in waves for a slack line cast similar to a wiggle mend.
By mending up and forward after the stop, you create extra space under the fly line.This is the mend you do to facilitate the tuck cast with a nymph or the pile cast with a dry fly. The tuck and the pile are the same cast with different result.
See illustration below. The tuck is the dark line and the the pile is the light line.
The tuck with a heavy nymph at the end of the leader causes the leader to flip under itself and drives the fly into the water with the leader landing upstream of the fly.
The pile is often confused for the puddle cast. The pile is performed with a long limp tippet so that when you do the overpowered forward cast and up and forward mend, the leader cannot flip over itself. It stalls over the target and the leader falls in a pile. The advantage is that it is more accurate a cast than the puddle especially when there is wind. Plus the leader lands first on the water and not the fly line as with the puddle. So the pile gives you better accuracy and a longer drag free float. But it is a more difficult cast to perform. Anyone can do the puddle.
I won't get into the curve casts but you get the idea. Learn what is possible. Then for the situations where you could not catch the catchable fish, practice that cast or mend.
The last time I went to the Madison River with my friend, we found a fish feeding in a slip in front of a rock but it was across a seam of very fast water. It was right in front of the rock in the photo below
I wanted to give him a shot at this fish. The pile would have been the best cast but I know this was a cast he could not make. So I told him to do a puddle.
He had never done a puddle cast. He had not heard of it so I told him how to cast and how to mend. He caught the fish on the second cast.
So this illustrates that to know what to practice, you need to know what is possible to practice. You also need to know when to use it.
Read, learn, practice, succeed.