If you are talking on religious subjects, avoid all cant. Cant words and phrases may be used in good faith from the force of habit, but their use subjects the speaker to a suspicion of insincerity.
Do not ask the price of articles you observe, except from intimate friends, and then very quietly, and only for some good reason.
Do not appear to notice an error in language, either in pronunciation or grammar, made by the person with whom you are conversing, and do not repeat correctly the same word or phrase. This would be as ill-bred as to correct it when spoken.
Mimicry is ill-bred, and must be avoided.
Sneering at the private affairs of others has long ago been banished from the conversation of well-mannered people.
Never introduce unpleasant topics, nor describe revolting scenes in general company.
Never give officious advice. Even when sought for, give advice sparingly.
Never, directly or indirectly, refer to the affairs of others, which it may give them pain in any degree to recall.
Never hold your companion in conversation by the button-hole. If you are obliged to detain him forcibly in order to say what you wish, you are pressing upon him what is disagreeable or unwelcome, and you commit a gross breach of etiquette in so doing.
Especially avoid contradictions, interruptions and monopolizing all conversation yourself. These faults are all intolerable and very offensive.