Remember that trout are more attuned to motion than any other potential sensory input, and use that fact to your advantage. Twitching your dry fly slightly on the surface makes that fly stand out from everything else --- twigs, leaves ---- also floating on the river's currents. Trout often respond well to this; sometimes even explosively --- hitting your fly in a seeming fury. The secret is not twitching too much. A properly twitched dry fly will move an inch or two and then come to a dead stop.With a few exceptions, yanking your fly across the surface 2 or 3 feet at a time is worse than useless and will often scare trout rather than attract them.