Good afternoon,
At some point, I want to do a more comprehensive post on fly selection. However, I in the few short moments I have to post today, I wanted to toss out two quick tips:
#1 You can't go wrong with Olive (or Black) below the surface
Both Olive and Black coloring have proven to be among the most effective in fly fishing. The reason is that across a variety of water conditions, these colors tend to present the best contrast to the water (in the eyes of the fish). There are times when red, orange, or flashier colors will certainly perform better, but this usually happens in extremely clear water. And while black or olive may not perform as better on a sunny day in a crystal stream or be the best every day otherwise, it is a good starting place almost anywhere you go.
#2 When in doubt use a more adaptive fly scheme
By this, I mean, if you aren't seeing any fish rising to an ongoing hatch on the surface and can't tell what critters they are sampling below the surface, choose a more amorphous, universal pattern, like a wooly bugger. In fact, many anglers I know have caught PR (Personal Record) fish on wooly bugger patterns. The good thing is that a wooly bugger can look like a lot of different foods that fish love to eat, including: crayfish, leaches, minnows, darters, sculpins and much more.
Hope this helped you out today!
Thanks for reading,
DT