There's no question we had a gold rush period with ebooks where the market was immature and both indie/self-published and mid-list authors could do well by advertising in the right places and taking advantage of certain Amazon features. As people should've expected things have changed as the market has matured. What used to work no longer does, and sales are down across the board with both professional and self-published writers I talk to. So in this ever-changing climate, what can authors do now to sell ebooks?
From my own experience, observations, as well as conversations with a number of other authors (and with a focus geared towards amazon), here's what I've seen in the area of mysteries, crime, noir, horror and thrillers (I can't comment about other genres, although my gut is fantasy & sci-fi ebooks are following along these same lines, and romance is a completely separate beast):
Advertising: Early on in the ebook era, advertising in the right places, like Kindle Nation, Pixel of Ink, and EReaderNewsToday could generate a flood of ebook sales, but their effectiveness over time has worn off. Right now Bookbub probably generates the highest number of sales, but their ads are expensive. Last year and early this year, you had a good chance of making money with a Bookbub ad, but now most authors I know who've used them over the last 6 months haven't broken even, and with the changes in Amazon's algorithms, these ads have become a losing proposition.
Free promotions: For a short time after amazon started their KDP Select program, they rigged their algorithms so that authors could generate a huge number of sales by giving away free books. After about four months of this, amazon changed their algorithms to make this less effective, and have since made further changes, both with their affiliate program and with their algorithms to make these free giveaways virtually useless. Originally they needed the free giveaways to help push kindle sales, but once they dominated the ebook reader market they needed to stop these free giveaways to keep ebook prices from moving to $0, and in effect, they've removed any value from authors now doing this. As far as free giveaways leading to future book sales by winning over new readers, forget it. Stephen Colbert recently joked on Colbert Nation how the kindle is a great device for storing 1000s of books that he'll never read, and kindle readers grabbing free ebooks are mostly hoarding 1000s of ebooks that they'll never look at.
Online book reviews: Web reviews seldom sell more than a couple of books--print or ebook the same.
Newspaper reviews: I've never been reviewed by the NY Times, so I can't comment on their effectiveness, but I have been reviewed very positively in the Washington Post, Boston Globe, LA Times, Orlando Sentinel, Newsdays, as well as others, both here and in the UK, Italy, Germany and France, and even rave reviews seldom sell more than a few hundred print books, and very few ebooks. The one place where I've been reviewed that does sell a lot of books is NPR.
While newspaper reviews might not sell a lot of books, one thing that they're very effective at is getting Hollywood to notice you.
Web short stories: I've never seen anything more than a small uptick in ebook sales from this.
Magazine & anthology short stories: I've gotten relatively small upticks in my Julius Katz ebook sales whenever Ellery Queen publishes a new Julius Katz story, but never more than 50 sales. I've gotten smaller upticks when I appear in print anthologies.
Social media: Social media might've worked early on in selling ebooks, but with 10s of thousands of authors doing it, it has long ago reached a saturation point and has no effectiveness anymore in selling ebooks, although it can still have a positive value in making more readers aware of you.
Killer cover: There was a time when a certain author was proselytizing that all self-published authors needed to be successful was a good cover and a good book description. Like any other snake oil, this sounded too good to be true, didn't it? Well, I doubt this was ever true--I think there were other factors on how Amazon could be gamed that contributed to early success of some self-published/indie writers, but to set the record straight, while an unprofessional cover might hurt you, a killer cover isn't going to sell anything.
Membership in a group to jointly market ebooks: I started Top Suspense with Ed Gorman and Harry Shannon because we thought that if we provided readers with a safe place to find high quality mysteries, thrillers, horror ebooks readers would gravitate to us. So how has that worked out? I think it has helped somewhat, but not as much as I expected. Where the greatest value with this group has been is to be part of a group of fellow pro writers for sharing information and ideas. From what I can tell, other groups that formed after Top Suspense have also had limited success.
Amazon: Bingo! Other than being a bestselling author, having Amazon promote you is the only clear way to sell ebooks now. Amazon has proven to be incredibly powerful in pushing ebooks--originally with ebooks that were triggered by their algorithms, and now the books that they're publishing and choosing to get behind. They've proven over and over again that they can sell 10s of thousands of copies through their direct marketing and recommendations.
Given all this, and given how unlikely it's going to be moving forward for a self-published/indie author to get Amazon behind them, it seems most likely that the vast majority of self-published/indie ebooks are never going to recoup their production costs (covers, proofing, formatting, etc.). So what should new authors and midlist authors do moving forward?
Face facts. The gold rush period is long over. More and more ebook sales are going to either writers Amazon's promoting or to bestsellers. If you're a midlist author, try to stick with traditional publishing, and if you bring back your backlist as ebooks, try to either contain costs, or go with someone like Crossroad Press who is able to make deals with B&N to feature their books. If you're a newer writer who is serious about having a writing career, keep working toward being published traditionally. It's your best chance of gaining real readers and establishing a career.