Take a look at Fly-Fishing Pressured Water, by Lloyd Gonzales, aka Gonzo. I've been tying his patterns, trying all the mayfly styles that seem appropriate for baetis.
Here is another, Rs2 style emerger I like, but I sometimes use a biot for the body. I like the tail sparse to imitate the shuck. This works as a wet fly also.
Hook- Tiemco 921 16-20. Measure this short hook to get the right size for the fly.
Tail-dun CDC or aftershaft feathers. Tie in a
Clump 3/4 as long as the hook shank and secure it at the
Bend of the hook. Wind the thread forward to form a thin tapered body.
Tie in a clump of stripped CDC or aftershaft feather to form the
Wing Sprouts. Or use CDC tips. The wing should be 1/2 the length of the hook shank. You can tie in longer and trim. Whip finish.
adapted from:
Little Lehigh Flyshop
scroll down a bit to find the original pattern