Eloquence is picked up more readily by those who read and listen to the words of the eloquent than by those who follow the rules of eloquence. (Augustine, doc. Chr. 4.8)Of course he was referring to preaching and rhetoric (Augustine was one of the great rhetors of his day), but the advice applies equally to the written word.
Actually, the advice is probably redundant for any decent writer. Certainly all the professional writers (of fiction) that I know became what they are because of their love of books. They could no more stop reading than they could stop breathing. By the same token, anyone who has to be told to get their nose out of the guides to writing a bestseller and read some good books instead will probably never be a good writer (successful, perhaps, but never really good because they write for the wrong reasons).