Here's something about how Brad DeLong did (does?) it:
[Andrei] Shleifer and DeLong’s freshman year roommate, Joseph Evall ’82, both say that DeLong was primed for Harvard, and that his reading ability left them in awe.
“He would read a book with lightning speed—far faster than any of the rest of us who were slogging through the material,” Evall says, “and he would retain 100 percent of what he read.”
Shleifer says that after seeing this, he thought DeLong was “some kind of a super-human,” but he realized later that DeLong just “knew how to skip pages.”
“Nobody ever told me about skipping pages,” Shleifer says.
Tyler Cowen, on the other hand, uses a different technique:
Another way to read quickly is to cut bait on the losers. I start ten or so books for every one I finish. I don't mind disliking a book, and I never regret having picked it up and started it. I am ruthless in my discards.
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All this is a good way to peddle my favourite quote from Woody Allen:
I took a speed reading course and read 'War and Peace' in twenty minutes. It involves Russia.