As you go about your everyday life, how many of the folks you interact with know that you're a writer? Unless you have an unlimited advertising budget, the only way people will buy your books is if they know you've written one. Even if you haven't actually published anything yet, it's not a bad idea to at least let people know you're in the process.
Obviously I'm not talking about going to the mall with a copy of your book in hand and walking up to strangers with a "Hey, I'm a writer. Would you like to buy my book?" You'll be lucky if they don't call security. What I'm talking about are the folks you interact with on a regular basis. I've been going to the same food market for years and most of the cashiers there know I'm a writer. I enjoy working on cars a lot so most of the auto parts stores in town also know I'm a writer.
Again, this was not a case of, in your face, "Hi, I'm a writer. Would you like to read my book?" Usually it would start with the typical cashier small talk, "Got anything planned for the weekend?" To which I would answer, "Not really. Just going to try and get some more writing done." "Oh, you're a writer? What do you write?" "Fantasies," I would answer. Either they loved to read fantasy themselves or knew someone who did.
Now that I can order copies of my book from CreateSpace, I've sold more to those folks and their family and friends than on Amazon. I'm still getting requests, all word of mouth, as more people read the story. I also made sure that the local librarian knows that I write. I've been in and out of the library enough that she recognizes me when I come in. She was more than willing to read my book to determine whether she wants to add it to the library's inventory. If nothing else, I know she will give me an accurate and fair assessment of my story.
Also because of word of mouth, I've been contacted by a woman who runs a small indoor farmers market style shop in the mall. She would like to set-up a small display of my books in her store. She hasn't read it yet but is interested because a friend read it and liked the story.
Bottom line, don't be afraid to talk to others about your writing and any books you may have published. Sure, there are always those who don't care or won't like your story, but it only takes a couple to like it and tell others. You gotta be your own advertising agency. Good luck!
Thanks for reading.