From the Art of Manliness comes The Unclassified Laws of Etiquette excerpted from a book published in 1880.
My favorites
Never point at another.
Never leave home with unkind words.
Never neglect to call upon your friends.
Never make yourself the hero of your own story.
Never pick the teeth or clean the nails in company.
Never fail to give a polite answer to a civil question.
Never appear to notice a scar, deformity, or defect of anyone present.
Never punish your child for a fault to which you are addicted yourself.
Never exhibit too great familiarity with the new acquaintance, you may give offense.
Never write to another asking for information, or a favor of any kind, without enclosing a postage stamp for the reply.
Never fail to say kind and encouraging words to those whom you meet in distress. Your kindness may lift them out of their despair.
Never refuse to receive an apology. You may not receive friendship, but courtesy will require, when a apology is offered, that you accept it.
Never fail to answer an invitation, either personally or by letter, within a week after the invitation is received.
Never give all your pleasant words and smile to strangers. The kindest words and the sweetest smiles should be reserved for home. Home should be our heaven.