When it comes to sales and promotion, DIY is not necessarily the best solution. It's much easier to promote somebody else's book than it is your own. It's also less likely to get you tossed in the spam hamper with Nigerian Princes and <Body Part> Enlargement Salesmen. For this, you need allies. Allies you can use to help promote your work to their audiences.
The best part of this? They don't even have to be aware of it. You can use the power of Amazon's ecosystem to promote your books on allied authors' descriptions. The catch? You have to promote theirs. The reality? It's going to happen anyway, you may as well take advantage of it.
The secret sauce is in the Also-Boughts. That magical ribbon of titles that shows up after you've sold a few books that says "Customers who bought this also bought:"
If you haven't got them, it's a function of sales over time. It's actually possible to go without sales long enough that they age out and go away. It's a good marketing ploy to try to keep that from happening by selling a few books now and again. The best way to do that is to publish another book, ideally in a series, but that's a different topic.
The beauty of the Also-Bought is that while your book points to somebody else's book, their book generally points back to yours. If you have a few pages of Also-Boughts, that's a fair number of people helping to support your title. You can help the process along by talking up their books. If there's somebody you'd love to have in your Also-Bought ribbon, you might get that person's latest book and read it. Assuming you like it and think your readers will too, then tell them about it. Write about it on your blog. Tweet about it on twitter. Add it to your Book of Face. Try to get more of your fans to buy it.
Once it gets ahead of a critical mass (the secret sauce of which is apparently guarded more diligently than the Colonel's Secret Recipe of Herbs and Spices), those books will start showing up on your ribbon and your books will start showing up on theirs.
You can also find allies on your Author Central page where Amazon helpfully tells people that readers who bought your books also bought books by a list of other authors. That's a great place to actually prospect for allies. You might write to one or two and tell them how much you admire their stories. Perhaps you can offer a pull-quote (sometimes call a "blurb") for their product description or cover copy. After a while, you might even ask them if they'd consider offering a blurb for your upcoming release. Some will say "no." Others will say "not this time." Some will say "sure."
The point is that other authors are not your competition when it comes to readers. They're your allies. Close bonds with allies can yield amazing results.
Offer to meet them in Yalta and see what they say.
Photo Credit: By U. S. Signal Corps - Library of Congress , Franklin D. Roosevelt Library & Museum http://docs.fdrlibrary.marist.edu/images/photodb/09-1905a.gif, Public Domain, https://commons.wikimedia.org/w/index.php?curid=211252