Knowing how to retrieve your flies can be more important than the fly itself. Imitative fishing involves moving the flies very little. The real thing tends to drift around somewhat aimlessly, and that is just what your flies should be doing. I believe one of the reasons for the effectiveness of dry flies is that anglers fish them static. If only they could do this with nymphs, and learn to recognize the takes, then they would catch far more fish.
When retrieving flies, put in plenty of pauses and expect fish to take then. A fish following a fly has two options when confronted by a fly which suddenly stops, one is to turn away, the other is to take. Very few can resist.
There are two other critical stages when fishing. One is the drop. As soon as the flies land allow them to swim all on their own for a little while and watch for signs of takes like a hawk. The other is the lift. At the end of the retrieve expect a following fish to take at the last moment. If he takes as you are lifting the rod, roll-cast into him.
This takes great presence of mind. Incidentally, the way it usually goes is that you pay great attention on the lift a dozen or so times and then on the thirteenth you become distracted by some nice looking woman, or man if you are a woman, and a ten pound fish comes along with all the goodwill in the world and you pull the fly straight out of his way. Bastard.