“Unlock Hidden Strategies: 18 Unconventional Tactics to Skyrocket Your eBook Sales on a Shoestring Budget!”

Make a habit of browsing it daily and if you see a request that you think your ebook is a good fit for, drop a comment suggesting it (don’t make it obvious it’s your own book as self-promotion is against the rules).
Or let’s say you’ve written a horror novel.
Subreddits like r/Paranormal and r/NoSleep are full of people interested in that genre who enjoy reading scary stories—so they’re good candidates for likely readers of your ebook.
Now, keep in mind that a lot of Subreddits and Facebook Groups have strict rules against self-promotion. So a lot of the time, you won’t be able to just create a post advertising your book. You’ve got to be sneaky about it.