Way back in the dim and distant past, when I was learning to tie there was one fly that my instructor used to judge my progress. It is very different to what you usually tie, and requires some finesse with the materials to get a good result. The Invicta. Its a very old wet fly from a famous British fly tier James Ogden. There are a couple of variations (well several really), silver, and pearly are the most commonly used variations.

Hook: Wet fly 8 to 14,
Thread: Brown.
Tail: Golden pheasant topping.
Rib: Gold oval tinsel or gold wire in smaller sizes. (Silver on the silver and pearly).
Body: Original was Amber seal's fur (you can use a sub). Silver is flat silver tinsel. Pearly is flat pearl tinsel.
Body: Natural red game palmered (as with all palmered hackles the number of turns of hackle should equal the number of turns of rib).
Wing: Hen pheasant paired slips, either from the centre tail or the wings. The wing is usually tied long, reaching to the tip of the tail.
Beard Hackle: Blue Jay (you can sub almost any blue dyed feather, Blue galina is the most common).

The Invicta represents a swimming caddis pupa, and is one of our most productive flies here. The silver can be more productive some days, it is a better fly for sea trout (sea run browns) than the original. To go fishing without a good stock of Invictas here is just, well, unthinkable.
Here's the original.

And the Silver Invicta.

(I know not a nymph but a challenge)

If you want a nymph you could try a really simple one. It is very simple, but again, it takes a little care and finesses to tie well. My variation on the PTN. The BiColour Nymph.

Or you could tie it reversed.

The reversed tied was a FOTW.

Those should keep your fingers occupied!

Cheers,
A.