How do you define success for an author? Getting an agent? Getting a book deal? Getting a second book deal? Keeping your agent and your publisher well into a lucrative career? NYT bestseller list? Keynoting writers' conferences? Some level of fame?
I define it like this: writing books you love and getting them into the hands of people who will also love them. And that I have done and hope to continue to do. What I write is not based on what is selling or trending at the moment. It's not the result of a formula found in a "how to plot a bestseller" book. It's what I want to read.
I never understand it when an author says he doesn't read his own books. If you don't even want to read them, why should I? I'm busy at the moment, writing another suspense title, but if I weren't...I'd gladly crack open one of my novels and I'd enjoy it. Why, everything happens just as I would want it to. What more can you ask for? Sure, I'm not surprised by it. There's no nail-biting, but there never is when you re-read.
Even though I meet less than half the above criteria for what makes a successful writer, I'm often asked for writing advice. And this is the best advice I can offer: write books that you love. Books you want to read. There will be others who will share your taste in reading materials and that will mean more than chasing a trend, a hot genre, or the ever-elusive book market.