From The Basic Manual of Fly-Tying by Fling and Puterbaugh
a basic adult mayfly imitation using hackle feather tips for the wings
Lay down thread base
Tie in dark hackle fibers for the tail, body length
Choose two hackle feathers in a light color for wings; measure the tips from behind the eye to the far end of the hook bend; strip off the fibers below the measured tip; tie in the wing a couple eyes length behind the eye; pull wings forward and thread wrap behind them to stand them up.
Take thread back to tail; dub in a body the color of a mayfly body stopping behind the wing
Tie in a dark dry fly hackle (1.25 to 1.5 the hook gap) behind the wings; wrap twice behind the wings and two or three times in front of the wings; tie off; pull back on hackle fibers to wrap the head; clip off extra hackle
Finish wrapping the head; whip finish; head cement