A favorite slogan of folks who pirate other people's work is that content wants to be free (as if books were zoo animals or something!). I don't agree with that; if I wrote it, I want to decide when it's free. Nevertheless, there are times when giving away content is a good idea. When you are an unknown writer without a publishing house behind you, being able to give away your work is actually a useful tool.
The trick is to give it away in such a way that readers a) know it's there and b) can get it easily. Thus, many more established writers rely on giving away their books directly. Their readers are already trolling their websites, so announcing that a DRM-free copy is available will get them lots of takers.
Those of us who don't have eager hordes of fans need an more direct channel. Amazon has a program called KPD Select that requires writers to make their ebooks available exclusively on Kindle for at least 90 days. Amazon then allows every participating writer to make their book free for 5 days during that 90-day period. They have an easy-to-use interface that lets you schedule the free days, one or more days at a time. The free period is supposed to start and end at midnight, Pacific time, but the KDP site warns you it can sometimes take a few hours to kick in.
The free day worked flawlessly for Where Magic Rules when I scheduled it to be free the first Friday in May. When I checked online, first thing in the morning, I had already given away 20 copies for WMR. For Shades of Empire, which was scheduled for yesterday, not one copy had been given away when I checked, even though the promotion showed as "ongoing" in my KDP author dashboard. When I went to the product page for SoE, I was shocked to see that the buy button still said $2.99 and there was still a "give as a gift" button (free books don't have that button). On the other hand, the book didn't have a sales rank, or a rank for "free in Kindle store," either. Having announced the freebie was coming on the eBook giveaways page on Goodreads (a useful site if you're a Goodreads member!), I was a tad annoyed.
Amazingly, Amazon had someone working on Saturday, and they advised me there had been a glitch. They promised to provide an extra free day to make up for it. Shades of Empire did finally become free at 5:00 pm, but of course, it didn't do nearly as well in its 7 hours as Where Magic Rules did in 24, except in the UK and Germany where the numbers were almost identical.
But, at some point in the future I will try again. If I weren't stubborn as hell, I wouldn't be a writer.