I've probably mentioned my love for the Snell Knot before. Without a doubt, it is the handiest and strongest knot I tie.
Check this out.
I've been experimenting with tandem flies. Two baits are better than one, right?
1) I tie the bottom fly as usual other than tying the head about 1/4" behind the eye of the hook then I snell the fly on to the leader.
2) I lightly wrap the tail and flash material to the second hook
3) Lay the partially tied fly on the leader at your chosen distance above the bottom fly and snell it onto the leader. (Start the Snell about 3/8" behind the hook eye to allow room for the collar and head.)
4) Tie a bucktail collar of the same or contrasting color, finish the head and cement.
5) Smear a little RTV sealer into the head of the fly and attach prismatic eyes.
6) Add a little more RTV over the eyes to assure they stay in place.
7) Go fishin'.
BTW, these flies are 4.5-5" long, tied on Mustad 34007 hooks. The Mono used is 30# Trilene XT.

Tied this way, the flies almost never tangle.
Fly ingredients.
Size 2-2/0 Mustad 3407 or 34007 hook
6 hackle feathers
Flash material (I used Christmas decorating stuff, darn near exactly like Flashabou)
Stacked Bucktail for the collar
RTV Silicone to shape the head. (DAP brand)
Witchcraft prismatic eyes.
Total time to tie, 15--20 minutes.
Applying the Silicone is a little tedious.
Allow to dry for about 30 minutes then go fishin'
If anybody wants to see the entire tying process, I'll tie a rig and photograph it in steps. (After I get in from fishing tomorrow.)