As a freelance writer, I have to deal with SEO all the time. But even when I'm moonlighting as an indie author, it's an issue. I found out why SEO matters to self-published authors. Have you?
SEO is search engine optimization. This basically refers to keyword usage in any given piece of text that's put on the Internet. When an optimal number of keywords are used in any article or blog post, that piece of content will be much easier for search engines to find.
When search engines can find you, readers can find you. This is why SEO matters to indies.
As an indie author, you should already have a blog. You want people to buy your writing, right? Well don't rely on your clever promotions and the reviews you can scrape together. Start blogging to get readers. If they like your blog, they will be tempted to buy your book. But once you start blogging, you've got to start thinking about SEO-ing (no...that's not a real word).
So here's the question you have to ask yourself: what are your keywords? Think about the words that people would use to find you and the keywords that you want them to use. Remember that the keywords you focus on must directly relate to your blog. If you're blogging about movies you like, focusing on phrases like "self-publishing" isn't feasible. Make a list of words that relate to you, your books and your blog. That's your focus.
Start optimizing your blog posts, and start getting more people to your blog. Once you're drawing readers in, you'll get more of them as long as you continue to provide content. People share links to blogs they like, and eventually word of mouth will help you gain new readers. But first, you need to throw some bait in the Internet waters...so get to cracking on those keywords.