Don't write on both sides of the paper to any but very intimate friends or relatives, they being disposed to tolerate slight departures from formality on our part.
Don't meddle with foreign nouns or verbs unless conversant with the language itself; incorrect and ungrammatical usage is too apt to be the unhappy result. Even foreign names and titles should not be used without the exactest care as to their orthography and application.
This rule should be especially remembered with reference to all matters destined to pass through hands editorial.
Don't erase misspelled words in letters of any moment. Recopy the entire missive.
Don't quote too constantly.
Don't underscore your words, unless they express something very important.
Don't send enclosures in a letter written by some one else; only the greatest intimacy can excuse this practice. Write your own letters and send in a separate envelope.
Don't write a letter in a towering passion; you would not care to have it confront you in some cooler moment.
Don't cross the writing in your letters. Life is too short and the time and eyesight of your correspondent too precious for this.
Don't fill up every available blank space and margin of your letter with forgotten messages. If these are very valuable, add an extra sheet to your letter, thus saving its appearance and the patience of its recipient.