Rusty Spinners can be a tough fly to fish mainly because they're so hard to see, as they ride low in the water and are generally fished at dark. This particular pattern helps to even the odds.
I'm going to tie this on a size 16 Dai-Riki #305 dry fly hook but you should also carry 14's and 18's. For thread, UTC 70 Denier in Rusty Brown is an excellent choice.
Start your thread on the hook shank leaving some space behind the eye and take wraps rearward before snipping off the tag, but save this tag end because you'll be using it later.
For the two tails I like Mayfly Tails in a medium dun. Separate 2 from the clump and pull them or snip them free. Don't worry about length yet, simply get them secured to the top of the hook with 2 or 3 thread wraps. Then you can pull the tails to the correct length, about 1 1/2 hook shanks. When you're satisfied with the length take thread wraps rearward to halfway between the hook point and the barb. To separate the tails a bit, lift them to vertical and then pull them apart to create some separation. It doesn't have to be much. Fold that saved tag end of thread around the bend of the hook and pull it up between the two tails. As you pull it forward, parallel to the hook shank, the tails should splay. You can then take thread wraps around the tag and the hook shank to lock everything in place. Continue taking wraps forward to about the 1/3 point on the hook shank before snipping the thread tag and the butt ends of the tails off close. You should wind up with the tails at about a 90 degree angle to each other.
Since the body of this fly is made of just thread, I like to add a bit of taper to it. Take a few wraps rearward and then wrap back up the hook shank. Wrap a little more rearward then back again. Repeat this process until the body tapers down from front to back. If you give your thread a counterclockwise twist and flatten it out, the wraps back up the hook shank should fill in any gaps and create a nice, smooth body. Once again end with your thread at the 1/3 point on the hook shank.
Standard white craft foam is used to create the fly's life jacket or PFD. A strip just slightly wider than the thickness of the foam is all you need. Pinch off one end of the strip to form a point and then cut off about an inch long segment for easy handling. This time give your thread a clockwise twist to cord it up and decrease it's diameter. Place the point of the foam strip on top of the hook shank and take nice tight wraps to secure it. The idea here is to build a little saddle into the foam on which the spinner wing will sit. Make sure these wraps are good and tight.
There are a lot of materials you can use for the wing but I've really gotten fond of white New Zealand sheep wool. It has a great natural appearance and floats well because of it's high lanolin content. A thin wisp, doubled over, is all you need. Twist the fibers to form a little piece of yarn and then snip off the unruly ends which tend to get in the way. Place the wool perpendicular to the hook shank in that little saddle and make criss-cross wraps with your tying thread to secure it. Again, make these wraps nice and tight. Advance your thread forward and take a couple of turns around the hook shank.
Fold the strip of foam forward over the hook eye and take a few tight wraps of thread to bind it down. Once the foam is really secured, you can sort of twist and pinch the foam off close. Getting the foam butt end completely covered can be a little tricky and probably doesn't matter much in the end but do your best.
With the head of the fly formed, do a 5 or 6 turn whip finish and snip or cut your tying thread free. Pull the wings to vertical and trim them to about a hook shank in length.
Head cement is a real good idea on this one. An ample drop that contacts the front of the foam and coats the head of the fly will do a lot for durability. When the cement dries, it will contract so the head of the fly won't be quite so bulbous. And that's it, the PFD Rusty Spinner. Yes, the foam helps with flotation but I include it because it makes the fly much more visible in low light conditions.