I had some success with a recent book promotion, so I thought I'd share my experience for my indie friends on these forums.
Recently, I moved Glyphbinder, Demonkin, and Bloodmender (my first trilogy) over to KDP Select, which means you get some additional benefits in exchange for selling your e-books on Amazon only. Glyphbinder was available on other platforms, but wasn't selling literally anything, so I figured, why not?
When you enroll in KDP Select, Amazon gives you two promotion options you can use once every 90 days. One of these is a giveaway, where you can make your e-book free for a few days and Amazon will promote it. This is the option I chose for Glyphbinder (my first book) and I timed it with a small ad buy at Free Kindle Books (
http://fkbt.com/ ), a mailing list with charges $25. The promotion actually worked really well.
With the aid of the FKBT add, I ended up with over 800 downloads during my giveaway period (4 days). In the month and change since, this has settled into a steady uptick in e-both book sales (Glyphbinder is the first book in a trilogy, leading to sales of the second two books) and a big uptick in Kindle Unlimited page reads (steady traffic for almost a month now, compared to 0 before). So, at least for a completed trilogy, this was a successful promotion by my (limited) standards, as the resulting sales and Kindle Unlimited reads will shortly pay for the $25 dollar expense and I may even make a small profit. The biggest benefit, obviously, was a massive (relative to prior readership) uptick in readers.
I don't know how effective this would be without a trilogy to sell, but I thought I'd share my experience since we have a number of indie authors on the boards.
In other news, I have three rejections on my current finished novel (another Supremacy book) and one agent bite so far.