Rocky Fork offers good fishing in May, with Callibaetis and blue-winged olives hatching all month, and maybe some damselflies by the end of the month. For the Callibaetis, try size 14-16 Callibaetis Cripples and Sparkle Duns. A size 18 olive Sparkle Dun, Baetis Cripple or Parachute Baetis should work for the blue-winged olives.
A size 8 damselfly nymph, such as Dougs Damsel or a Marabou Damsel, is also a good choice this month. Late in the month there might be some adult damselflies around. If so, try a size 6 Braided Butt Damsel or equivalent; adult damsel patterns don't always entice trout, but when it works it's pretty cool.
Olive scuds, Brassies, flashback Pheasant Tail nymphs, and Hares Ear nymphs are good sub-surface choices. Small scuds, about size 16, work best at this time of year.
You might see some caddis this month. If so, try size 16 Sparkle Pupas in the afternoon and early evening; fish them on a dead drift just below the surface if you see swirls from feeding trout.
Watch for rattlesnakes and take precautions against ticks. After a day of fishing, do a strip search for the latter. You can find them anywhere, but be especially attentive to any folds of flesh or hairy places, and your back. Carry a tick removal kit and know how to use it.
This isn't a big water, and you may encounter crowded conditions on the weekend.
For more on May tactics and flies, see the Rivers in General forecast