My own experience & history as a published author.
I've been a published author on & off since 2001 with I would say moderate "success". Here are a few things I've "learned" from being a published author on how to "sell" books during that time.
Social media doesn't work as well as one might think.
One writer said that social media like Facebook & Twitter may account for less than 5% of their overall book sales. I myself have sold MORE books BEFORE the advent of so-called social media.
You can sell a ton of books if a "celebrity" endorses them.
Ian Fleming's James Bond books didn't start selling until JFK endorsed them. Likewise with Tom Clancy's debut novel until Ronald Reagan publicly endorsed it. And who can forget Oprah's Book Club!
Even bestselling authors aren't sure how to sell books.
50 Shades Of Grey author E.L. James said in an interview how "shocked" she was that her books sold. Bridges Of Madison County author Robert James Waller said he couldn't "believe" his success.
You can try the Wattpad/Fanfiction.net route to get noticed.
50 Shades Of Grey initially started off as Twilight fanfiction on Fanfiction.net. Likewise, other bestselling authors got "noticed" on Wattpad. I myself have started writing fanfic on Wattpad.
Why do some books become more successful than others?
Some authors "promote" their books extensively and they still don't sell many books while other authors post their books on, say, Amazon and they become instant bestsellers on the very first day.
So why does an author NOT sell a ton of books anyway?
One "theory" I've read time & again about why certain books DON'T sell is that people are turned off to social media posts that scream "Buy my book!" that they feel are little more than spam.
What other writers have said about the profession . . .
One writer said they didn't really start selling books until they started publishing more books. Another writer said it was "persistence" more than talent that helps make a writer successful.
In short, there's NO magic bullet to selling tons of books.
That's basically it in a nutshell. I think that's ONE thing that ALL the writing "experts" CAN agree on. And, if there is a "magic bullet" to selling tons of books, I sure haven't found it yet!
The good news AND the bad news . . .
The good news for authors is that there are MORE opportunities to get your work out there than what there were when I first started. The bad news is you STILL have to find a way to sell them!
The bottom line is, keep writing and be persistent.
This is perhaps the BEST writing advice I can give. And, if anyone can give me ANY suggestions on how to sell MORE books, please feel free to mention them in the "comments" section below. Thanks!