It's incredible that this 1916 tutorial on how to think, by none other than Henry Hazlitt, would still hold up after all these years. But here's why. Hazlitt was largely self-educated. He read voraciously. He trained himself to be a great intellect. In the middle of this process, he discovered that it is far more important to learn to think clearly than to merely take in information. The result was this book.
In some ways, it is a course in logic. But more than that, it is a training manual for how to fire up and manage one's mental energy.
He discusses how to think about analogies and discover their errors. He speaks of the error of too much aggregation and misplaced definitions. He presents the rules for the interplay between theory and example. He shows how to spot errors in theory and experiments. He shows how to think all the way to the end of a problem. He gives some very practical advice on the relationship between thinking and reading - and how to plan that reading so that one uses one's time well.
His examples of how to think and how not to think are lucid and compelling. His influences in this little book include Stanley Jevons and Herbert Spencer, so we can see here that Hazlitt was already steeped in economic literature when he wrote this book in 1916.
It remains an excellent primer in how to gain, and make use of, a good education.