It's been a little while (since Spring) for me on Valley. So I am not up on the latest trends.
There are BWO's in the spring (March), and the fish get on them. Usually the same streams have decent fall hatches too, but not sure on Valley. There are virtually always a few midging fish in a few select holes. Same holes every time. These are typically flat water pools and are best avoided. I only go to dries on Valley when a more major hatch, like BWO's, get them coming up in a little faster water.
In my experiences, the fish on Valley are fairly spooky, which is compounded by the fact that it's a slow, shallow, flat, and clear stream. Stealth is indeed the key. In low conditions, my fish usually come in bunches. i.e. 8 times out of 10 I spook the hole before catching anything! But the other 2 times I might pull 3 or 4 from that pod.
They are not overly selective. If you can present something without spooking them they'll take. Exact matches and perfect presentations are not necessary. I generally do ok with standard stuff like a bead head hare's ear.
The biggest piece of advice is that it comes up, and falls, unbelievably fast after a rain. The "easiest" time to fish it is typically