Lead wire can be used to get a taper.
The trick is to flatten
one end of the the lead wire. Get a pair of needle nose pliers
with a flat sections just before the cutters.
Start at the back of the hook and wrap the flat end of the lead and you will get a taper up to the thicker round lead.
The second trick is to use the right tying thread and for tapered lead bodies, I have found nothing better than Uni-Stretch
. It is a nylon tying thread/floss that stretches with tension. Plus you can unwind it a bit and it lies flat. So you can wind thin flat stretch layers or thicker round layers.
For the initial over wraps of the lead wire, wrap across the lead wire or the thread will fall into the grooves between the lead wire and not over-wrap the lead. You'll see what I mean when you begin wrapping over the wire.
Any material like copper wire that is placed on the hook before the lead should extend all the way up the body of the hook. If you just tie it in at the end of the hook, it will create a "bump" at the end of the hook that destroys the natural taper of the body. The lead goes over this consistent diameter from tail to head.
Although it is recommended that the diameter of the lead wire be about the diameter of the hook, what is more important, IMHO, is that the fly look realistic. For the fly above I used wire that is much thicker than the hook because the natural nymphs are plump.
Some flies call for lead wire tied along both sides of the hook to get a flat shape for stonefly nymphs. The rear edge of lead wire should be flattened to create the taper of a natural.
Heres another tip about wrapping lead wire behind bead head nymphs. Most modern beads are countersunk so the rear hole is larger than the front hole. Most often the directions will tell you to coat wrap the bare hook with tying thread and then wind the lead wire. If you do that you cannot slide the lead wraps into countersunk space of the bead. For my first fly, I will try wrapping the lead on the bare hook and see if it will fit into that space. It makes for much more stable bead that cannot slide back and it add a bit of extra weight without changing the shape of the fly.