How do I find good keywords?

So for marketing https://joinpageturner.com/?ref=indiehackers.com, my plan is to start by posting the best posts on Pageturner daily to different social channels (FB, Twitter, IG).

I plan on acquiring followers by searching for various keywords related to Pageturner, and engaging with the tweets that come up, where I can add something meaningful.

How do I find these keywords, or better ways to engage? I tried "books" and "reading", but nothing really good shows up.