Sometimes it's just as simple as posting about something to promote it.
You might be already doing it, but not about your books. I know I didn’t. Some people even don't know I've written books. And that shouldn't be the case if you're publishing your fourth.
So, as soon as you're starting to release your first, and especially if you already have a book, start talking about it. You can't talk too little about it. People are not going to get tired of it. And those who will, aren’t your audience.
When they think about you, they should think about your books.
At some point, you'll even notice it's going to be the other way around. People first come across your book, that's the first association. Then you as the author follows. Some of them will not even bother to look you up. They're happy with the book on itself. Whether you wrote it or somebody else doesn't come to mind.
Let's give the book more importance, more life. More visibility, just by sharing about it more. It's really as simple as that.
I understand the thought that might come to mind: what difference will it make? You might not have too many followers, or don't see why it would lead to more downloads. Still, just start doing it. It's free and it will set interesting things into motion. Things we simply can't foresee.
The book is already available, even if it hasn’t been published yet. Now it just needs to live alongside everything else you share.