Select a quality streamer hook in a small to medium size.  I find that long shanked streamer hooks in sizes larger than 6 tend to sink "bend down" in an unnatural manner.  When tying featherwing streamers I tend to stay in the size 10 to 6 range.  Above and below these sizes I'll opt for a bucktail conversion.

Start by laying down a base of fly tying thread.  If you intend to tie a "presentation" quality fly, use white thread and make a very smooth underbody.  It will make a big difference in the final appearance of the fly.  For fishing flies I tend to be just a little less demanding.  A spiraled base of black thread makes a durable foundation.  Tie on a bunch of peacock sword fibers that are about 1.5 times the hook's gape in length.

You can use Uni-Stretch or a similar synthetic material.  I am using a Rayon floss in the fly pictured.  To keep the floss from fraying while being wrapped, I use a bobbin to apply the floss body.  After tying in the floss, half-hitch the tying thread several times and cut off.  Wrap a neat, tapered floss body and use a two turn whip finish on the floss itself.  Then tie the working thread back on and wrap back over the two-turn floss knot.

The floss body should extend to a point just past the mid-point. The rear two-thirds of the body is floss, but you need to leave room for the wings, hackle and head.  Hence the body is really tied on 3/4 to 4/5 of the actual hook shank length.  I like to use three or four layers of floss for a nice, thick tapered body.

Tie on  six to eight quality peacock herls.  I break off the fragile tips by pinching them between my thumb and finger.  Tie the hurls from front to back, then pull out a length of tying thread.  Twist the herls around the thread to make a peacock herl chenille.  Wrap forward and separate the herls from the thread and tie off securely.

Select a pair of hackles for the wings.  The wing can extend to a point even with the tail or just slightly longer.  The more you go beyond one and a half times the shank length, the greater incident of fouling the wing on the cast   Select feathers with a well defined center line and rounded tips with fine stems.  You'll have to shop a bit to find a quality Silver Badger cape, but Furnace is relatively common.  For a top grade streamer neck expect to pay $20 to $40.  Get the best you can, it will last for many seasons with proper care.

Tie in a fold a hackle collar with barbs that extend to the back of the peacock.  Tie in and sweep back.  Form a neat thread head and coat with Sally Hansen's Hard-As-Nails.