I was quite fortunate to have an AP English teacher my senior year of high school that understood this advice, and expounded on it often. I recall that he boiled it down to one simple line:
Garbage in, garbage out.
What he meant by that was that it's not enough to simply read. You have to read high quality literature if you want to become a writer. You can't expect to read nothing but news, comic books, National Lampoon, MAD magazine (and in our era, blogs) and become a good writer. It just doesn't work that way. It's like trying to get physically healthy by eating junk food.
Garbage in, garbage out.
What he meant by that was that it's not enough to simply read. You have to read high quality literature if you want to become a writer. You can't expect to read nothing but news, comic books, National Lampoon, MAD magazine (and in our era, blogs) and become a good writer. It just doesn't work that way. It's like trying to get physically healthy by eating junk food.