As has been previously said- the most important point is getting your fly in the zone most likely to illicit a grab.
The rest of the pet theories work because that is what the angler believes will work and they fish with confidence. Many times I have been caught up with the adrenaline of a good fish thinking "Aha, I am on to something" only to have it exploded shortly there after. Changing colors, sizes, etc. to conditions just will not significantly change your odds. If you stick to what you believe, and make consistant changes to what makes sense, then you will have results that are consistent to those changes. If you get in a mood and do it all backwards, chances are you will get the same results as your normal routine.
Put your mind to work and think about every move you make. Don't just autopilot because what worked an hour/day/week ago might not be best for the current set of variables. If you always do the same set of moves you might, or might not, be taking the best approach. The only way to find out is to experiment and constantly push your personal envelope. If it was always about catching fish, bait is a hell of a lot more effective.
I look back at one of 'those' days winter steelheading. The fish were in this run thick as thieves and on the grab. Between the four of us we caught the hell out of them using different flies and tips of various sink rates/lengths. The one thought that constantly comes back to me? Why did I not try a waked dry over them? Or why did I not go after them with a traditional 'greased line' presentation? These fish were holding in less than three feet of water that was perfect with a touch of green. Probably would not have worked, but the world will never know. If I am ever lucky enough to encounter such a situation again, my first two passes will not be to get the fly too deep.
I have three words: presentation, presentation, presentation.