One of the things I learned pretty quickly from my first eBook was the importance of "promotion." I've worked in sales (telemarketing no less) before, but am kinda gun-shy about yapping about me. And my writing. This GR author blog is and was a good first start. However, these things can either turn into a way too general (and not useful) "indie book advertising" guide or a rant about a specific bad idea that blew up in your face.
In trying to strike a balance, here are my thoughts on formal advertising.
PPC can be very, very useful. I ran Google Ads, I tweaked key terms, and I did very well. On a very modest three figure budget, Google moved books. I chose the Amazon Kindle edition as my target link because Amazon controls a huge chunk of the ebook market. Lots of folks have Amazon accounts. I also included the term "ebook" in the ad, so as not to confuse anyone.
I even created an Excel spreadsheet to keep track of books sold with vs. without Google Ads. I then created an even more narrow field of days with ads vs. without ads. Google Ads correlated with sales. The conversion rate for different words and days varied, but that's life. Google moved books pretty close to instantly and consistently. I will be using them again.
I noticed a truism of all book sales - they move best around December/January (holiday time) and in the summer. During the fall, folks are too busy sipping hot cocoa to buy and read a book. During the spring, they are too horny to see straight.
I also tried some other sites. I tried an ad on my beloved Reddit. Reddit instantly moved people to the Amazon link, but the conversion rate was close to nil. The PPC cost was also higher than Google. Reddit and subreddits allow you to find a really cool niche, but I'm not sold they have the cash to splash on a book. In fairness to Reddit, I only tried a few days and not during peak book-sale season.
I tried an ad on one of those "Kindle Review" websites. It moved a single book and cost way too much money. If you have your own website and twitter feed, I'd recommend against it. These sites may work wonders for free and $0.99 books, but my $5.99 price tag may not have gone over well with the normal readers.
I did not try Facebook. I liked the ability to target on Facebook, but the PPC cost was a bit high AND I'm not sure anybody buys anything from a Facebook link.
I did use this very website here: Goodreads. And I was and am a happy camper. Goodreads does not give you same the instant movement as Google: lots less pageviews and whatnot. However, the conversion rate was pretty great. Folks either bought the book or added it on Goodreads. Does it offend you to be reduced to a number as a "conversion rate"? I'm sorry. I owe you a coke. I will, however, be using Goodreads for ads again.
In terms of non-direct promotion, or, rather, informal advertising, I posted a link to the Amazon sales on my twitter handle and the top of my website. The twitter handle probably moved some books. Twitter, of course, was super useful when I first launched the book.
I also wrote and write lots of guest posts at great sites: some of the kind editors allowed me to include a link or mention of my book. Others did not. The book mentions in guest posts definitely moved some books. Thank you, Fox Soccer, Dirty Tackle, and others. I also owe you guys a coke.