...common sense and TACT.
Ooooh, boy. Tact. That's a toughie.
I observe that there is much involved in comunication that takes tact out of the hands of the author. More so than in speech, tact, in print, bears very much upon the reader; their mindframe, predelicitons, preconceptions of the author, whether they agree or disagree... Arguably, with a reader of sufficiently contrary nature, no author has a chance of conveying an idea with "tact". This is not to say that the effort ought not be made, only that, despite your dilligence, there will be times when a reader defeats all your efforts at tact, and you find yourself assailed in spite of your best intentions.
Such is part of rhetoric and oratory...