According to some indie authors, it’s the only thing. If you have a “good” marketing strategy, you’ll sell lots of books. Not only does this philosophy lead to some strange behavior, some of it is counter-productive, in violation of various media sites’ TOS, or just contrary to common sense. Even a sound marketing strategy, with a couple of ads, and a significant but not intrusive media presence won’t do you any good unless… Drumroll, please.
You write a good book. It doesn’t have to be War and Peace, but it should match reader expectations. It should be free of significant spelling and grammatical errors. It should conform to genre expectations in some degree. It should tell a story in a straightforward fashion without awkward POV switches, plot holes, random characters, or any of the other ills that fiction can be subject to.
There are people for whom writing a good book is almost instinctive, and a somewhat larger number who will never be able to write a decent one unless they hire a ghost. There are also quite a few people who have the germ of a good book, or at least a not terrible one, but seem to have been investing their energy in almost anything besides working on their craft.
Write the best book you can. Send it out to your beta readers. Work on it some more. Send it to the betas again. Have it professionally edited (and pick your editor with care, because there are frauds out there). Then, publish it.
Or, and here’s a novel thought, submit it to a publisher. There are many, many misconceptions about publishers and I’m not going to address all of them, but here are a couple that I run into constantly. I am amazed by how many people believe that it is standard practice for an author to pay a publisher. It is not. Presses that charge writers to publish are vanity publishers. There are a handful that are honest about what they are, and are reasonably reputable, and far more who masquerade as selective publishers, and are frankly scams.
You don’t pay agents up front either. Like your publisher, they are paid out of your book sales. And in many cases, you don’t need an agent. Many, many reputable smaller and e-publishers take unsolicited manuscripts. All publishers are out to make money, but that doesn’t mean that they aren’t receptive to new talent, and small publishers are often more writer-friendly than the big guys, if less generous with advances.
There are many valid reasons to choose self-publishing, but it is not necessarily the best choice for many writers. Personally, I choose a combo of self and traditional, because sometimes I need to write things that don’t fit anyone’s idea of “marketable” and I want that voice to be heard, but I’m also intent on this as a career, and the professional advantage that the traditional publisher gives me is invaluable. There’s no question this approach lets my less quirky stuff enjoy a broader audience, and I make much more money off it than I do off the self-pubs, even with the lower percentage of profits.
Most writers I know of, and all that I know personally. who make real money off their books are at least partly traditionally published. There are a handful of indies, some of them extremely talented, who have been very, very successful, but I think it’s a harder row to hoe. Personally, I’m a writer, not a PR person, a cover designer, a copy editor, a formatter, or a proofreader. However many of those hats you wish to wear, if you are an author, you must be a writer first, not as an afterthought.