Back when I was trying to write indie scripts (gay cowboy YEARS before Annie Proulx!) in a factory town (L.A.), it was the Rise of the Screenwriting Teacher: anybody with a masters degree and good stage presence was charging rubes like me hundreds or thousands of dollars for advice about how to break in to the smoking hot spec screenplay market. I moved to L.A., took the "MFA Lite" version of UCLA's film program (just the screenwriting instruction, none of the filmmaking), and attended every seminar I could afford.
I was deep into the first stage of advice, the Sponge Stage. Luckily for me, I ran across the genuine article, a real screenwriting mentor, a wonderful instructor and a truely kind person, Neil Landau. Without him I would have probably given up on every kind of writing. A maelstrom of advice flew around my head. Neil's gentle guidance served as anchor points--I could feel the truth in his observations, even if I didn't always know how to do as he suggested. It was a frustrating but also thrilling time.
Alas, I was not meant to live in Los Angeles, and ran scuttling home after having won some minor awards but without ever having anything sold or produced. But I didn't stop reading all the advice I could get my hands on, even as I turned away from scripts and toward novels and short stories. Eventually, I realized that much of the advice out there was contradictory. So many theories--3 acts, no, there's 5, or 7. Or, there's only 3 plots in the universe, no 7, no 23 (23?)...it couldn't all be true. Kind of like growing up without any religion--how could I possibly pick one?
This was the beginning of stage two, the Bitter Kitten stage. Often accompanied by a resurgence in whatever bad habits haunt your life (in my case, Snack Cakes and Too Much Television), Bitter Kitten stage often involves ceremonial discarding of advice books, tapes, and whatever projects you've been working on. Take it from me, toss out the books and tapes, but keep your rough drafts.
At this point you might find yourself obsessed by a Holy Grail of writing--for me it was voice. What is voice? When will I know I've got mine?
I felt lost and alone in this stage, abandoned by my early studies, but without a theory of my own. However, if you can stand the discomfort of muddling through this stage, which by my observation is unavoidable unless you are smart enough to never have sought advice in the first place, better days wait for you. Once you start writing every day instead of reading advice all the time, the most lovely thing happens.
You start to pick and choose among the things you've read. Maybe you'll decide that McKee knows nothing about act structure, but is pretty sharp about characterization. You might decide that it doesn't matter how many beats are in a scene, or scenes in a sequence, or sequences in an act, or acts in a novel. You content yourself with noticing when you've created a successful one of any of those things. Maybe you half-remember something you read in Egri's book (you have read Egri, haven't you?), you might mangle it until it makes sense to you.
This is the third stage, Chrysalis. The shell of your daily writing practice protects you while you spin your own theories--at first out of the pieces you've broken off of others, but as you pick up speed, read a lot more, and try to apply your theories to new works or your own works, you begin to build your very own theory and beliefs about what makes a good story, why some characters leap off the page at you, where things need to speed up or slow down in your stories. It was somewhere in this stage that I realized both Egri and Aristotle were probably wrong--neither plot nor character were more important than the other. Rather, they were two aspects of the same thing, like matter and energy. Each affects the other, and a flaw in one becomes a flaw in both. But I'm still working on that theory!
And then, one lovely day, one of my critique partners said, "The voice in this story is perfect." That's when I tumbled into the fourth and final stage of advice, the Poetics stage. Like Aristotle before me, I'd hit upon a set of theories, suspicions, beliefs, and guiding principles that worked for me. I was ready to hear other theories, weigh them against my own beliefs, and refine my poetics as I learn from other peers and the great writers of the ages. Reading became a sort of virtual salon.

Or, at writing conferences, in the bar, especially late at night, an actual salon. If you can get people to stop talking about ebooks and Amazon long enough to get a real conversation going, that is...
No one theory out there can possibly tell you how to write the stories that only you can tell. Voice isn't so much the result of things you do, as it is the absence of all the junk you know enough to discard--what's left is your voice, and it was there the whole time. You just couldn't hear it for the noise.
No matter which stage you are at in your writing adventure, Sponge, Bitter Kitten, Chrysalis, or full-grown Poetics, never forget. Theories and advice should never rule you. Take what you need and leave the rest. And if you see me in the bar, the next one's on me!