I'm not talking about an entire language necessarily; even just a a single concept will do. I'm actually writing a Tagalog grammar book to learn Tagalog grammar better, which is way over the top I suppose. But how about explaining something to a toddler as suggested by the Feynman Technique?
1. Choose a Concept
2. Teach it to a Toddler
3. Identify Gaps and Go Back to The Source Material
4. Review and Simplify (optional)