I'm an Independent Author and I try and participate in as many avenues of promotion as I possibly can, but no matter what I do the best promotion I can possibly get is reviews and word of mouth. Now you can't force people to do reviews for you, no matter how hard you try, but you can ask. It never hurts to ask. I write reviews for every book I read and I make sure to tell people what I'm reading at Goodreads by using their "Currently Reading" button, and by mentioning it in any group that I'm in that has a "currently reading" discussion thread. I really want to emphasize the importance of making those simple entries in groups and hitting the "currently reading" buttons because a lot of people see those posts and if the author you're mentioning is an independent author like myself you're opening them up to larger audiences who might not find them otherwise. Whenever I do a review at Goodreads I make sure that the buttons are pushed that share that review at Twitter and Facebook, so all those people that follow me see which authors I'm reading, with the hope that they will in turn check those authors out.
Through Goodreads I've found a lot of other Independent Authors that I really enjoy like Sharon Stevenson, Ken Pelham, Garth Perry, Russell Blake, ML Dunn, Robert Pruneda, Patrick Jones, and James Somers just to name a few. I really enjoy the Independent Author's writing style because it hasn't been run through the grinding mill of a publishing house that strips down language, characters, and story lines to try and give the reader the publishing houses's version of what a good book is. Independent Authors step out on a limb and give you the raw, unfiltered, and completely imaginative books that they intended the reader to have, as opposed to giving up their story and their rights to a publisher who will make it their version of what they think it should be, which in many cases is a far cry from what the author intended. I'm of the firm opinion that as more and more readers find Independent Authors they are going to enjoy those unique and unfiltered voices much more than the mashed down, bland, publishing house books that they've been forced to read over the years. But the key to having the opportunity to read these Independent Authors is supporting them. I've reviewed all the Independent Author's books I've read, and many of them have thanked me for my reviews, which is something you never get from mainstream authors, and some have in turn reviewed my books. As independent Authors we appreciate the time and effort it took to write our books and we know the value of acknowledging each other. Now I'm not saying in any way, shape, or form that we should just rubber stamp each other with five star reviews, because it hurts our credibility as reviewers and mistakenly awards authors who need to do some more work to bring it up to that five star standard. But I am saying that we should support each other. When we post tweets we should re-tweet each other, when someone re-tweets you, you should go out of your war to re-tweet them. When someone reviews you, you should return the favor, and even if you have no interaction with an author at all, if you enjoy a book you need to post a review for them because thats the best possible thing you can do for them to show your appreciation for them providing you with a pleasant reading experience.
Simply stated, spread the word. A simple mention at Facebook, Twitter, Goodreads, or in your own blog could be the one mention that helped readers find an Independent Author. And finding readers to read our books really, really makes Independent Authors, like myself, very, very happy.