Best way to study a single book in depth — not just reading through?

I've been reading through the Bible cover to cover using this app which has been great for building consistency. But I'm realizing I want to go deeper into certain books — really understand the context, the structure, the themes.Does anyone have a method for deep-diving into a single book? Do you use commentaries? Outlines? Study the historical background first?Would love to hear what actually works for people who aren't just speed-reading.