An effective way to become an expert on a subject is to write about it every week for a few years. The process of writing crystallizes the essentials of a subject matter. Even better, it helps if you integrate the Feynman Technique:
- Choose a concept and write it down
- Explain it in very simple terms (as if to a 6 year old)
- Identify gaps in knowledge whenever you start using jargon
- Crystallize and simplify.
Repeat the iterative ladder ad infinitum.