Here's a great pattern that works well when fished alone, and when used as the top fly on a dry/dropper rig. I've caught trout on it during a PMD hatch on the Missouri River, and closer to home on the Musconetcong River during terrestrial time. The fly works just about everywhere there are trout, and will also take panfish and bass.
Hook: TMC 100 # 12
Thread: 3/0 Danville yellow monocord
Tail: Moose body hair
Hump and Wing: Elk body hair
Hackle: Dry fly - one brown and one grizzly
Tie them in sizes #10-16. You can also use red or green thread to change the view, or any other color you may wish to try your luck with.