Al's Trico by Al Miller of Pennsylvania is one of the most effective Trico patterns ever. It also happens to be relatively easy to tie, even in the smallest of sizes. When trout get fussy during a trico hatch, it's often a matter of size, and smaller flies usually win out.
Here I'm going to tie an Al's Trico on a size 24 TMC 100 dry fly hook. As you can see here, the size 24 is dwarfed by a size 12. Take note of how much thicker the wire is on the 12. Although I usually use the vise jaws to mash the barbs on hooks, I like to use very fine needle-nosed pliers for hooks this small. If you have midge jaws for your vise, by all means use them.
For thread, I'm going to use black UTC 70 Denier. Load it on a small midge bobbin if you have one. Start your thread at the halfway point on the hook shank and take wraps rearward to about the hook point and then snip the tag end off close. Wrapping back to the bend, cover up the tag and wind your thread forward to just behind the hook point.
Although this is a size 24, you want to use slightly oversized hackle, here, size 20 from a Whiting 100's pack. Although the original pattern called for grizzly hackle, and I'm going to use it here, I really like the look of light dun a little better. It's up to you.
With the shiny side of the hackle facing towards you, pull down about 1/8th of an inch of fibers at the butt end. With your tying scissors, snip these fibers off close to the stem then strip another 1/8th of an inch of fibers from the top to ensure it wraps correctly. Tie in the hackle stem with a few tight wraps of thread.
To beef up the thorax of the fly a little bit, I like to use just the smallest amount of black dry fly dubbing, here, Wapsi Super Fine. Go very light, just a few fibers are all that's needed.
The dubbing noodle should be short and just barely cover your tying thread. Wrap the dubbing around the hook shank to form a bulbous little thorax. With that done, begin wrapping your hackle, 3 or 4 turns are all you need. Secure the hackle with 2 or 3 turns of tying thread and then pull the remainder of the hackle and the hackle fibers rearward and take a couple more wraps of tying thread. You can then snip the remainder of the hackle off close.
Do a 5 or 6 turn whip finish to secure the tying thread and elongate the body of the fly. You can then cut or snip your tying thread free.
The pattern fishes fine just like this, but many anglers prefer to trim the bottom hackle fibers off so the fly rests in the film. I usually carry both. Once again, I like this pattern with dun colored hackle like those to the right and at the top but there's certainly nothing wrong with grizzly hackle either. I've heard some anglers will leave the tag end of their tippet untrimmed to give the impression of a long split tail like on the naturals. This is 7X which should give you an idea of just how small this fly really is. It's a great pattern, give it a try.