One of the good ways to master a skill is to start teaching it to others.
One method for studying a book very well is to plan ahead before reading it to teach it after you complete reading. This will make you super attentive while reading. The process of teaching in itself will also make the knowledge you have gained from the book become strong in your mind.
Teaching is the last and final phase of learning without which the learning process is not complete. Teaching closes the loop. Therefore it is a good idea to start teaching others whatever useful skill or knowledge you have for this would boost your mastery level of such skill or knowledge.
Have you ever found yourself mastering something after you have explained it to others? What was it?