If you want to master what you learn, learning and productivity expert Elliott Masie says "teach it to someone else" in an article he wrote for Chief Learning Officer magazine. 
When we approach learning something new knowing that we'll have to explain it to others, we're most likely to be more active and engaged in mastering the new content.
The moment we take something we learn to explain it to someone, we go through an internal process, Elliott shares citing a research study by the University of Minnesota. 
We try to simplify the content by restating it in our own words, sometimes even sketching diagrams to facilitate the transfer of knowledge. Then as we teach and listen to ourselves, we clarify what we learned and feel more confident about what we know.
Paraphrasing Elliott, teaching creates a post-learning experience that cements the new content.
To make teaching-to-learn a regular practice in your life, here are some ideas you can try. Start a blog or a podcast; join a Toast Masters Club, book club, or a study group; or organize a lunch n' learn with friends or colleagues at work.
Any of these will put you in front of someone you can teach.