I often forget key plot points and character details from fiction books I've read. What strategies can I use to improve my retention and get more out of my reading?

I read fiction regularly for leisure, but I find that after finishing a book, I quickly lose track of important elements like character arcs or thematic details. I've tried skimming back through chapters, but it's time-consuming and doesn't stick. Are there efficient techniques or tools that can help without interrupting the reading experience?