I am a deviant. While I am familar with a lot of patterns I almost always simplify. I try to think more about the bugs or creatures I am trying to suggest,and how they move or weather they need to be shallow or deep rising or falling etc. These article s by Al Campbel are a great read:

http://www.flyanglersonline.com/alcampbell/ac061603.php

http://www.flyanglersonline.com/alcampbell/ac100603.php

When i first started tying ( before computers and internet were in common use) I tryed to
copy patterns from pictures in my Joe Brooks fly fishing book. Unpressured Brook trout in the UP of Michigan ate these flies with relish.( Of course now I understand they would have eaten almost any fly the right size.)

When I lived out west in Denver caddis and small mayflies dominated my home waters.
There were certainly lots of other bugs that showed up seasonally ,but day in day out the 2 categories mentioned were available to the fish

Now in my oklahoma home waters crayfish and small fish dominate our basses diets usually in heavy cover so it dictates the flies we use. Our trout fishing is in tailwaters below damns,and midges small minnows dominate. In one of our areas caddis and mayflies are also very important ,although they are 2 or 3 shades lighter in color than thier western cousins