Practice, Practice, Practice. The bottom line is my flies are never up to the standards I try to hold myself to either. For example, the hackle was too long in the picture I posted earlier of a Catskill March Brown I tied. Will it catch fish? Hell yea it will - which is why I didn't toss it. I noticed it and adjusted on the following flies. Someone had mentioned it before but when you tie a particular pattern, tie a dozen. Each fly will get better and better and better. I should also mention that after you tie your first, reference one that someone really good tied and adjust your proportions, body thicknesses, etc. on the 2nd fly. Then do the same for the rest.
Most importantly, don't give up. It will start to click after some time.