Never stop testing, and your advertising will never stop improving.
Advertising is a business of words, but advertising agencies are infested with men and women who cannot write. They cannot write advertisements, and they cannot write plans. They are helpless as deaf mutes on the stage of the Metropolitan Opera.
Advertising people who ignore research are as dangerous as generals who ignore decodes of enemy signals.
Never write an advertisement which you wouldn't want your family to read. You wouldn't tell lies to your own wife. Don't tell them to mine.
Hire people who are better than you are, then leave them to get on with it. Look for people who will aim for the remarkable, who will not settle for the routine.