This is a really big one guys, but I will do my best to answer from my own experience as a self-published author.
Without the backing of a major publishing house, you’re pretty much left on your own.
Personally, I publish my books through Kindle Direct Publishing (KDP), a service for self-published authors that Amazon offers. Since that is my primary avenue for selling my books, I’ll start there.
KDP offers two free forms of promotion for your eBooks that you can find under the Promote and Advertise link in your dashboard: Kindle Countdown Deal or a Free Book Promotion. The countdown deal allows you, for a limited time, to reduce the price of your book. The free book deal, also limited by time, is self-explanatory. Either option will increase units sold, with or without additional advertisement.
In addition to the free services, KDP also offers the option to create a paid ad campaign. I’m sure you’ve seen the pop-ups on Amazon recommending other purchases you might like to make. It’s not cheap, but it works.
After utilizing those resources, I move onto my social media accounts (Twitter, Facebook, etc.) and list my new promotions. People are eager to get something for free at a hugely reduced price, so the free advertisement here increases units “sold.” Personally, I have never tried to use Twitter’s paid promotion services, but I do use Facebook. Again, it isn’t cheap, but it gets the word out there.
Word of mouth is also a powerful tool. When I run a promotion, I try to tell everyone I see. People tend to enjoy meeting and talking with an author and are more apt to buy after the interaction. Asking a stranger what they do and following up by telling them that you are an author with books on promotion can lead to quick sales.
Even when you are giving your work away for free, you can gain huge benefits. People talk with their friends and family about what they like. If they enjoyed your book, then more people will buy it. Plus, if you’re really lucky, they might even leave a positive review.
Another great promotional resource for writers is Readers’ Favorite. If you submit your work to their website, they will find a professional reviewer to go through it and rate it. If the review is positive enough, you will receive the Readers’ Favorite 5-Star Seal, an emblem and accolade that you can add to the cover of your book. If you click on the links, you can read their 5-Star review of my first book, Rebirth, and my second book, The Drift.
Finally, I flood the free websites for book promotions with my offering. Normally, I skip over the ones that charge a fee, but you may decide to pay for gained attention. Here are a couple of links to give you the idea: Kindlepreneur and TCKPublishing.
One final note: Don’t forget about the impact of book signings! Most local libraries have reading clubs and most booksellers will let you set up a table for free. This is a chance to not only sell your books but to meet your prospective readers.
I hope this helps! Keep writing and don’t forget to subscribe to the monthly newsletter and post alerts.