When you're an indie author, you have to be your own publisher, literary agent and biggest fan. In other words, stop being humble. You are an amazing writer and anyone who isn't reading your book is totally missing out. Remember that. Write it down if needed. Keep it close by...and when all else fails, just pretend. Because if you're going to promote yourself, you have to be capable of selling yourself.
You don't have to convince readers to buy your books, whatever they're about. You have to convince readers to buy you as an author. That's the real secret to selling books. So first things first: convince yourself that you are awesome. If you can't do that, you certainly can't convince anybody else.
Fooling yourself is an important part of being an indie author. But there's no reason to be ridiculous about it. Read and re-read your book. Check it, double check it, triple check it for errors. Make sure there are no plot holes or glaring grammar mistakes, no crazy punctuation and no excessive junk you don't really need. Once you feel comfortable that you have done the best you possibly can, there's no reason not to get out there and start marketing yourself and your work with absolutely everything you've got.
Now's the time to drop all pretense of being humble. Tell everyone about your book, and that it's great. Write down a few short, concise sentences that sum up what your book is all about. Repeat them, memorize them, and use them when people ask (and even if they don't).
Tweet about your book...every single day. Write Facebook updates about it. Blog about it. Guest blog about it. Look for book review sites, and sell it to them -- at least once a week. Post excerpts of it. Find Goodreads forums where you're allowed to talk about it. Give the damn thing away, always reminding everyone how fabulous it is. Once you get some reviews, make a list of all the good quotes and share them all over the place -- with a link back to the book, of course.
And meanwhile, conduct yourself like a professional author. You are always selling yourself as an author with everything you put out there, and you should always be in a mindset that you are an amazing one.