Some gems from “Writing a Convincing Editorial” by Robert Tracinski:
The single greatest error made by beginning writers is that they try to say too much. This error comes from the belief that, in order to be convincing, an argument must be utterly comprehensive, addressing every possible issue that relates to it. But no argument is effective unless it can be absorbed and remembered by the reader. An effective editorial must be essentialized, focusing only on the most important issues and integrating them into one graspable whole.
[…]
The primary goal of one’s writing is to be clear: to convey one’s conclusion and the evidence for it in a manner that the reader can easily understand. Eloquent phrases, vivid images, and humorous examples are only valuable if they advance that goal.
The article goes on to cover in some detail on the following guidelines:
1. Focus on a central theme.
2. Know the viewpoint you have to refute.
3. Make inductive arguments.
4. Base moral evaluations on the facts.
5. Rely on the reader’s implicit knowledge and values.
6. It is more important to be clear than to be eloquent.
7. End on a call to action.
8. Good writing comes from exhaustive editing.
Well worth reading [Link].