August Birch here on Medium has some pretty great advice about how to leverage IG for the fiction writer.

It’s mostly about engaging with people who you think would be interested in your work, as a person, not just ‘but my book’

His advice is to follow the bookstagram tag and find accounts there that fit your genre, genuinely engage, post your own reading, etc and build a following of your own from there.

I believe I got all that (in paraphrased) from his 1k tribe class which he offers free.