Good resources for mastering SaaS user engagement?

Trying to get much more intentional about user engagement – by which I mean measuring and optimizing for experiences that SaaS users find useful and that encourage deeper exploration of a platform (paid users, no ads).

I feel like we have bits and pieces of it that we've grown organically, but it's still very ad hoc and unrigorous.

Looking for recommendations on books, conferences, training programs, Slack groups, forums, etc – really anything that would help a team grow their skills in this area, understand what's possible, established patterns, and best practices.