The single best way to learn is...
Is to teach someone else! The thought is not new. Lazslo Bock in his new book "Work Rules!" reports that Frank Oppenheimer, the younger brother of the noted physicist J. Robert Oppenheimer purportedly said that "the best way to learn is to teach." Lazslo goes on show that Google (where he headed up People Operations) takes it literally.
In order to help another to learn the teacher has to understand the subject, then think through how to present it to others. Some have a difficult time (see previous posting on Experts), since they do things intuitively. But this forces even an expert to reexamine the subject from a different perspective.
It gets better if you twist the word teach. In adult learning it is said that we don't teach, rather we "help someone to learn." Children have to be taught and motivated through the process. Adults are typically motivated themselves and have experience at learning. Therefore, we are merely "helping them to learn," when teaching adults. Looking at it that way gives an altruistic frame to the process.
Bock goes on to point out at Google they have a similar motive. He writes, " Giving employees the opportunity to teach gives them purpose. Even if they don't find meaning in their regular jobs, passing on knowledge is both inspiring and inspirational." And it helps cement the subject in the teachers' brain.
Have you noticed it when you are called upon to help someone to learn?