For me, a Rusty Spinner is often the last fly I'll tie on, in the dark, at the end of the day. It's important the fly have the proper silhouette and that it floats well in the surface film. I have a lot of confidence this pattern does both.
Although you can tie a Rusty Spinner in a wide range of sizes, a 14, in general, just seems to get the job done. Here I'm using a Dai-Riki #305 dry fly hook. Mash the barb and get the hook firmly secured in your vise.
Snip a 4 to 5 inch length of tying thread and set it aside for safe keeping. Then, start your thread on the hook shank just above the point. Here I'm using Rusty Brown UTC 70 Denier. Take wraps back to the bend.
Separate two microfibbets from the clump. I really don't think color matters much. Measure them to form tails that are 1 1/2 to 2 times the length of the hook shank. With a few wraps, secure them to the top of the hook. Then pull them forward and take one wrap of tying thread underneath to kick them up. This should cause the two fibers to split slightly.
Now pick up that piece of thread you set aside and fold it around the bend of the hook like so. Bring both legs of thread up between the two microfibbets and then pull them forward to split the tail. You can then take a couple of wraps of tying thread to lock the tails in a splayed position. Snip the butt ends of both the microfibbets and the thread off close. You should end up with something that looks about like this.
For the body of the fly, I like rust colored Super Fine Dry Fly Dubbing. Pulling just a small amount at a time, form a nice thin dubbing noodle on your tying thread. Begin wrapping the noodle around the hook shank so the dubbing starts right at the base of the tail. Keep taking wraps to form a thin tapered abdomen. Remember it's always easier to add a little more dubbing than it is to take dubbing off. You should end with your tying thread at approximately the 3/4 point on the hook shank.
For the wings, I really like polypropylene, mainly because it floats so well, but don't go overboard with the amount of material. Just a quarter of a strand of polypropylene yarn will do it. Find the midway point on the segment that's about an inch and a half long. Secure the segment to the top of the hook shank. Then, with cross wraps, get it into a position perpendicular to the hook shank. Add a little more dubbing to your thread and then take cross wraps over and below the wings to build a plump little thorax.
With this done, secure your tying thread with a 4 or 5 turn whip finish and snip or cut your tying thread free. If you have any errant fibers now is a good time to cut them out.
To trim the wings to length, pull them up and back and snip them off using the far back end of the hook for measurement.
The finished fly should look about like this. Oftentimes, while the fly is still in the vise, I'll apply floatant and work it in to the body, wings and even down the tails to further ensure the fly won't sink.
There are so many ways to tie a Rusty Spinner but I think the most important part is having confidence in the pattern you choose to tie.