Do not be hectoring or arrogant. Those who disagree with you are not necessarily stupid or insane. Nobody needs to be described as silly: let your analysis show that he is. When you express opinions, do not simply make assertions. The aim is not just to tell readers what you think, but to persuade them; if you use arguments, reasoning and evidence, you may succeed. Go easy on the oughts and shoulds. ( Telling people they are talking nonsense is a bit of a turn off; and does not further the debate.)
Do not be too pleased with yourself. Don’t boast of your own cleverness by telling readers that you correctly predicted something or that you have a scoop. You are more likely to bore or irritate them than to impress them.
Do not be too chatty. Surprise, surprise is more irritating than informative. So is Ho, ho, etc. ( Hmm, don’t agree with this one at all, but I suppose it wouldn’t go down too well on the Economist)
Do not be too didactic. If too many sentences begin Compare, Consider, Expect, Imagine, Look at, Note, Prepare for, Remember or Take, readers will think they are reading a textbook (or, indeed, a style book).