Decorum

We've been having fun peeking in an 1879 copy of Decorum (subtitled A Practical Treatise on Etiquette and Dress, with no author listed) recently. It's interesting to see how times have -- and haven't -- changed over the last 130 years. From the chapter on "Conversation":

Let your conversation be adapted as skillfully as may be to your company. Some men make a point of talking commonplaces to all ladies alike, as if a woman could only be a trifler. Others, on the contrary, seem to forget in what respects the education of a lady differs from that of a gentleman, and commit the opposite error of conversing on topics with which ladies are seldom acquainted. A woman of sense has as much right to be annoyed by the one, as a lady of ordinary education by the other. You cannot pay a finer complement to a woman of refinement and esprit than by leading the conversation into such a channel as may mark your appreciation of her superior attainments.

Subjects to be Avoided
In talking with ladies of ordinary education, avoid political, scientific, or commercial topics, and choose only such subjects as are likely to be of interest to them.

Talk to People of their own Affairs
Remember that people take more interest in their own affairs than in anything else which you can name. If you wish your conversation to be thoroughly agreeable, lead a mother to talk to her children, a young lady of her last ball, an author of his forthcoming book, or an artist of his exhibition picture. Having furnished the topic, you need only listen; and you are sure to be thought not only agreeable, but thoroughly sensible and well-informed.

Avoid talking too much of their Professions
Be careful, however, on the other hand, not always to make a point of talking to persons upon general matters relating to their professions. To show an interest in their immediate concerns is flattering; but to converse with them too much about their own arts looks as if you thought them ignorant of other topics.

Slang
Remember that all "slang" is vulgar. It has become of late unfortunately prevalent, and we have known even ladies pride themselves on the saucy chique with which they adopt certain cant phrases of the day. Such habits cannot be too severely reprehended. They lower the tone of society and the standard of thought. It is a great mistake to suppose that slang is in any way a substitute for wit.

Using Proverbs and Puns
The use of proverbs is equally vulgar in conversation; and puns, unless they rise to the rank of witticisms, are to be scrupulously avoided. There is no greater nuisance in society than a dull and persevering punster.

Witticisms
Do not be always witty, even though you should be so happily gifted as to need the caution. To outshine others on every occasion is the surest road to unpopularity.

Interrupting a Person while Speaking
Never interrupt a person who is speaking. It has been aptly said that "if you interrupt a speaker in the middle of his sentence, you act almost as rudely as if, when walking with a companion, you were to thrust yourself before him, and stop his progress."

Avoid Unfamiliar Subjects
Never talk upon subjects of which you know nothing, unless it be for the purpose of acquiring information. Many young men imagine that because they frequent exhibitions and operas they are qualified judges of art. No mistake is more egregious or universal.

Interjections
The interjection of such phrases as, "You know," "You see," "Don't you see?" "Do you understand?" and similar ones that stimulate the attention, and demand an answer, ought to be avoided. Make your observations in a calm and sedate way, which your companion may attend to or not, as he pleases, and let them go for what they are worth.

Conversing with Ladies
If you are a gentleman, never lower the intellectual standard of your conversation in addressing ladies. Pay them the compliment of seeming to consider them capable of an equal understanding with gentlemen. You will, no doubt, be somewhat surprised to find in how many cases the supposition will be grounded on fact, and in the few instances where it is not the ladies will be pleased rather than offended at the delicate compliment you pay them. When you "come down" to commonplace or small-talk with an intelligent lady, one of two things is the consequence, she either recognizes the condescension and despises you, or else she accepts it as the highest intellectual effort of which you are capable, and rates you accordingly.