Learn by Teaching
The best way to learn is by teaching. It seams that when we teach others we actually learn because teaching is way of transmitting information in the most optimal way and in order to do that, our brains engage with the task to simplify the information and to find the most important bits that are necessary to unfold the rest of it that follows, as such, we learn.
As an experiment, do the following: Pick a topic you know nothing about and study it for a short period of time. Make sure that you pick something that is pretty hard for you to comprehend at first. Now, try to teach your wife/colleges/kids of what you have learned. There is a good chance that by the time you finish your first lesson, you will have a better idea of the topic than you had before.
Is it coincidence that most of the best minds of the past century were also teachers and they were constantly involved with public speaking engagements, seminars, etc? I think not! Of course, most of them were related to the world of academia that also contributed to developing their intellect.
Although teaching is a way of learning, not everybody is good at teaching. This is another skill of its own.