From an undated but late Victorian self-help / etiquette book called Don't: A Manual of Mistakes and Improprieties more or less prevalent in Conduct & Speech (Ward, Lock, London circa 1900). The author is noted as 'Censor' and some of the advice still holds, e.g. bores, exaggeration etc., as for the 'scandals of the hour' - it would now be considered very dull NOT to be able to discuss them...more to follow.
DON'T talk over-loud, trying to monopolise the conversation.
DON'T talk to one person across another.
DON'T whisper in company. If what you have to say cannot be spoken aloud, reserve it for a suitable occasion.
DON'T talk about yourself or your affairs. If you wish to be popular, talk to people about what interests them, not what interests you.
DON'T talk in a social circle to one person of the company about matters that solely concern him and yourself, or which you and he alone understand.
DON'T talk about your maladies, or about your afflictions of any kind. Complaining people are pronounced on all hands great bores.
DON'T talk about people who are unknown to those present.
DON'T be witty at another's expense; DON'T ridicule anyone; DON'T infringe in any way the harmony of the company.
DON'T repeat the scandals and malicious rumours of the hour.
DON'T discuss equivocal people, nor broach topics of questionable propriety.
DON'T dwell on the beauty of women not present; on the splendour of other people's houses; on the success of other people's entertainments; on the superiority of anybody. Excessive praise of people or things elsewhere implies discontent with people or things present.
DON'T introduce religious or political topics. Discussions on the subject are very apt to cause irritation, and therefore it is best to avoid them.
DON'T give a false colouring to your statements. Truthfulness is largely a matter of habit. Where very few people would deceive or lie maliciously, many become wholly untrustworthy on account of their habit of exaggeration and false colouring.
DON'T interrupt. To cut one short in the middle of his remarks, anecdotes or story, is unpardonable.
DON'T be disputatious. An argument which goes rapidly from one to another may be tolerated; but when two people in company fall into a heated dispute, to the exclusion of all other topics, the hostess should interfere and dexterously banish the subject by introducing a new topic.
DON'T be long winded. When you have a story to tell, do not go to every detail and branch off at every word – be direct, compact, clear, and get to the point as soon as you can.
DON'T cling to one subject; don't talk about matters that people generally are not interested in; DON'T,in short, be a bore.