I've offered featherwing salmon fly classes in the past at a shop in the Seattle area and a shop in Port Angeles when they were owned and run by friends of mine. I'll see if I can get one of the Seattle shops to offer a call again because I'm sure there are others beside yourself who are interested in tying them.
Describing how to set a married wing is not an easy thing to do. But I'll give it a go:
1) When setting the wing is compress it as much as you can with your thumb and forefinger of your right hand while holding the wing very securely against the hook and tie down area with your left themb and forefinger.
2) Use the "loose loop" technique to make your first wrap of thread and do not loosing your grip of the wing from your left thumb and forefinger as you slowly pull the "loose loop" tight by pulling up on your thread on your side of the hook after the loop is formed.
3) When the first "loose loop" of thread is pulled tight (remember it is done by pulling up on your side of the hook), take a second "loose loop" with your thread just in front of (toward the hook eye, but not over nor behind the first wrap) and slowly pull it tight by pulling up on your side of the hook (just like you did with the first wrap). This should nearly have the wing compressed. Remember to keep you left hand thumb and forefinger tightly holding the wing as you do this.
4) Take a third "loose loop" just in front of the first 2 and pull it tight by also pulling it up on your side of the hook. These three thread wraps will have sompressed the wing as much as it will be compressed and are the key to a good wing set.
5) Make three more tight wraps of thread and place the first of these directly on top of the last wrap you did in step 4 and the other two in front of it toward the hood eye. DO NOT LOOSEN YOUR GRIP ON THE WING WITH YOUR LEFT HAND AND THUMB UNTIL AFTER THESE THREE WRAPS ARE MADE!!! Also, these wraps are also pulled a little tighter by pulling up on the thread after each is made.
6) At this point, you can take your thumb and forefinger off the wing; but do not move the wing or it will be moved out of position since it is held in with only 6 wraps of thread and it can pivot.
7) Take a look at the wing to see if it is setting on the top center of the hook. If so, do nothing, If not, place your left thumb and forefinger tightly on the wing at the tie down area to hold the wing together and then adjust the wing either to the left or right by using the thumb and forefinger of your right hand to "gently" (and I mean gently) move it a little bit in the direction you need it to move. Remember, this simply rotates the wing around the hook and that you cannot move the wing front or back without destroying it.
8) After the wing is placed on the top center of the hook, take 2 more very tight wraps backward toward the hook bend over the very last thread wraps you made. IN NO CASE ALLOW THREAD TO COVER THE FIRST TWO THREAD WRAPS YOU MADE WHEN SETTING THE WING OR IT WILL DISTORT THE WING AND DESTROY IT!
9) Leave the wing stubs alone at this point and go on to tie in the cheeks, topping, and horns (in that order) before cutting the wing, cheeks, toping, or horns stubs off. AND NEVER COVER THE FIRST TWO THREAD WRAPS YOU USED TO TIE IN THE WING OR IT WILL DISTORT THE WING!
10) Now you can carefull cut the stubs of the horns, topping, cheeks, and wing. As you cut the stubs, KEEP THE WING HELD TIGHTLY IN YOUR LEFT THUMB AND FOREFINGER! Also, proceed slowly and only cut a few fibers at a time in order to make the stubs as short as possible without cutting you tying thread (or you will feel like crying if you do).
11) After all the horn, topping, cheek, and wing stubs are cut off, finish the head by putting a drop of medium viscosity head cement on the butts (or stubs) and then carefully cover the stubs with flattened tying thread until you have a nice bullet-shaped head. AS YOU FORM THE TYING THREAD HEAD, HOLD THE WING TIGHTLY WITH YOUR LEFT THUMB AND FOREFINGER TO PREVENT IT FROM BEING DISTORTED.
12 Upon forming the head, whip finish, cut the thread, and then cover the thread with medium viscosity head cement. It usually takes 2 or 3 coats of medium viscosity head cement to get a nice, glossy head. Loon's Hard Head in black is a very good cement to use to finish the fly because you can finish the fly with the white or light yellow thread you should have tied it with and not have to change thread to finish the fly and still have the desired black head most of the classic flies used.
I sincerely hope this verbal description helps you and all others who are having trouble with setting and tying in mixed wings on full-dressed featherwings.