It is as harder to break out on Social Media than in a small group, like, say a writing group or a forum. Basically, you need to plug into an existing community if possible, get linked with other people. Going to any Social Media platform alone, relying just on tags is hardly going to work.
And, yes, like with ALL platforms, the earlier you start there, the more audience you will have. The latecomers are always left in the dust. So, don't expect miracles.
So, there is a couple of threads right now to link up with other Tapas people, try follow for follow to start with, and once your feed starting to build up, note the tags people are using.
As a novel writer, I feel your pain about images. What writers do with some degree of success is create moodboards with quotes and post quotes of the reviews received.
Twitter is more text-friendly than Instagram, but it still loves the pictures. On Twitter you count on your pinned post as well to generate interest in your work.
I hope this helps! I know how hard it is, because, yeah, I am only preparing to besiege the Instagram atm.
For example, this is what I am hoping to share on Twitter tomorrow as a quote from my book with a link attached and some silly text in the post: