Hendrickson nymph and imitation.
If you live anywhere near my latitude (Western NY approx. 42 degrees) you still have a few weeks until the first major mayfly hatch... this does not mean the fishing stinks, it actually means the opposite! The fishing this time of year can be incredible (no fisherman + plenty of food = successful fly fishing)... so find out what is going to hatch in your local stream, and use the appropriate nymph. The best way to do this is to take stream samples so you can accurately match the nymph size and color. Why does using nymphs before the hatch work? Since the mayfly emergence is approaching the nymphs are fully mature, and becoming more active... some will begin to drift in the current, and that's why trout are keying in on them already. Do a little research, tie up some nymphs, and go catch some trout!