I've been seriously writing with the aim of being a published author since 2002, when I quit my "day job" to concentrate only on my writing, something my wife thought at the time thought also meant "unemployed deadbeat." It wasn't until ten years later that I managed to find a NY agent I "clicked" with. During the intervening time, I wrote a lot. I used to track my word counts and, two years running, I hit over a million. So, when my agent asked to see my work, I sent her sixteen finished novels. It took her another two years to sell one. DREAM WITH LITTLE ANGELS remains my most successful book to date.
I don't write crazy amounts of words anymore. These days, my year totals are more like 250,000 by the time you count first drafts, rewrites, short stories, etc. Currently, I have over ten books published, some traditionally through Kensington Publishing, NY, some self-published under my own imprint DangerBoy Books.
Right now, my agent is shopping two manuscripts for me and I am about to dive into the fifth Alvin book for my series with Kensington. I have the prologue completed and plan to toss together a short proposal to go along with it.
Throughout my writing career, I have deeply studied my craft. Not only through writing books (I own over three hundred of them, yet I doubt I'd recommend more than a dozen), but also through retreats, seminars, and workshops. In particular, the one-week short story workshop and two-week masterclass I attended through Kristine Kathryn Rusch and Dean Wesley Smith were most valuable. I learned more in those three weeks than the rest of my life combined. I consider Kris my mentor.
Whatever else I know came from simply writing a lot. The more prolific you are, the more practice you get, the better writer you become. It's a simple formula, just not necessarily an easy one to follow. The key: stay on the path.