Stef, on behalf of Rebecca/RHBookish:
Well thanks! Glad to have you. 
I’m actually not good at what I would consider “community building activities.” I don’t enjoy hanging out on social media, I feel awkward around large groups of people, etc.
Plus, I also don’t have enough free time to handle the kind of tasks that fall into that category along with everything else I do to write the books and run the business. But that’s why I hired the lovely Stefanie, who has strengths in the areas I lack and can help take some of the burden off my shoulders.
With her help, we’ve finally got the Alcove open, and I’m hoping for it to grow into something truly amazing, where like-minded people can come and talk about the stuff we all enjoy.
But back to your original question.
In many ways, this community just grew around me as I was writing and posting this story. Being consistent over a long period of time certainly helped to grow my following.
Having stuff available for cheap or free has also made a big difference, because it lowers the barrier to entry and means more people may try my stuff and have a chance to fall in love.
Also, you know, consistently advertising my books (paid advertising) draws more people in in the same way, and some of them stick around.
I try to be authentic and reasonable online, and I enjoy thoughtful discussion, so I’m likely to dip in and participate where and when I see it.
Really, I’m just lucky in many ways.