The term "ethos" comes from the classical Greek rhetorical tradition. It is linked to our modern English word "ethics," but it also implies a wider range of qualities: character, position in a community, and personal authority. Therefore, a persuasive writer establishes ethos in his or her work through showing or demonstrating each of these things.
To write ethically, one does not plagiarize. One also gives full credit to all sides of an argument, including those arguments with which one disagrees.
To show character, one is fair and inclusive.
To show position in a community, one includes references to shared values and shared sources of authority (a Christian might quote the Bible, for example), but also by using shared language patterns.
To show personal authority, one includes references to experience or credentials that apply. A major league baseball player might mention playing in the World Series, for example.
In short, in relation to 1984, one does the opposite of Newspeak.