Know Your Enemy

Know your audience. Sounds a little bit like "Know your enemy" to me. The writer is the competitor, the audience is the judge. That's not to say the writer and the audience can't be friends... just a friend that the writer really wants to impress. Or maybe they don't want to be friends; maybe they want to hate each other (see comments on political Youtube videos).
Assuming they want to be friends, the writer and the audience need to get to know each other. The audience gets the easy half of this. They read what is written. The writer has to put a little more thought into it. Who is the audience? What do they care about? The broader the audience, the more difficult it becomes. The writer must respect the audience, but can't go overboard and turn the writing into an unintelligable cacophony of technobabble or newspeak. Often as not the writer also must justify the price of the magazine or the book in the reader's hand. "Do unto audiences as you would have them do unto you." A golden rule for writers or just friends.