Hook:

18 - 22 Tiemco 100 or other standard TDE dry fly

Thread:

8/0 Uni-Thread Olive, Grey or Rust

Wing:

Medium Dun polypropylene yarn clipped to leave a wing butt and pitched forward 45 degrees

Tail:

Mayfly Brown straight zelon

Body:

BWO Olive Superfine, Beaver or Zelon Dubbing

Hackle:

Light Dun clipped flush with hook point

You can also tie this fly with a black or white polypropylene wing.  The black wing is easier to see in low light situations.  I like to use the Rust colored thread as it resembles the buggy dark red eyes on the natural.  Another option is to use a Tiemco 101 straight eye hook in the smaller sizes to expose more of the hook point.