The pale morning duns have started their hatch season. Yellow sallies are another strong hatch this month, and you might find a few golden stoneflies around; the latter won't last much longer. Caddis hatches will be building.
For the PMDs, you might reach beyond the standards and try some local patterns, such as a Burks Hunchback Infrequens in size 16-18 or a Barr Emerger in size 18-20 for the emerger stage; the GitterDone is another good choice. You could also try beadhead Pheasant Tail or Hares Ear nymphs in size 18 to imitate drifting pre-hatch PMD nymphs. While a PMD Cripple or Parachute PMD in the same size can work during the hatch, you might do better to stay with the nymphs as trout will feel more secure if they feed subsurface during the middle of a bright July day. When the sun is high, you will find the most receptive trout in shady areas.
When yellow sallies are on the water, adult imitations can be productive; sunny days are best for these bugs. The best yellow sally adult imitations rest in the film, not on top of it. Don't ignore the nymph stage of this small stonefly. For tips and some fly ideas, see Beyond the Big Stones.
During the evening, expect caddis activity. Pupa and diving patterns (Sparkle Pupa, Z Wing Caddis, Diving Caddis, Soft Hackle, etc.) will fool fish during the early stages of the hatch. Tan is always a good color choice. As the evening wears on, trout will become more receptive to surface patterns. Black size-18 caddis are also a possibility at this time of year.
Near the end of the month, hopper patterns such as a Parachute Hopper will become effective. Craneflies can also be a factor in late July, as can tricos.
For more on July tactics and flies, see the Rivers in General forecast