Here, match size and color as closely as possible. I have taken my nippers and cut down hackle, tails, whatever to get a fly down closer to the size that is flying, or mashed down and rubbed some river mud on a dry fly to make it just barely float in the surface film to resemble an emerger. Instead of getting geared up the instant you park your rig, walk down to the water, find a place to sit, and watch the activity for five minutes. Longer is probably better, but being anxious to fish, even five minutes seems like a long time. Watch for birds working.
Birds swooping low over the stream is sure proof of a hatch, mating flight, or spinner fall.
Birds working higher may indicated a mating flight is happening - and later, toward evening a spinner fall of the females laying their eggs, and the exhausted males falling to the water on the water will bring the fish up to feed. L ook for any fish activity. Those are fish which are taking nymphs or emergers before they reach the surface. The fish don't break the surface, but make a small hump or bulge in the water. Eventually, those insects will make it to the surface and you will have a hatch - and a place to use dry flies.