Letter-writing is a subject of so varied and extensive a nature, that it can scarcely be reduced to rules or taught by precept; but some instructions respecting it may afford assistance in avoiding error, and obtaining a degree of excellence in this most important exercise.

When you write a letter to any person, express the same sentiments and use the same language as you would do if you were conversing with him.  “Write eloquently,” says Mr. Gray, “that is, from your heart, in such expressions as that will furnish.”

Before you begin a letter, especially when it is on any occasion of importance, weigh well in your own mind the design and purport of it; and consider very attentively what sentiments are most proper for you to express, and your correspondent to read.

To assist invention and promote order, it may, as some writers on epistolary composition recommend, occasionally be of use to make, in the mind, a division of a letter into three parts, the beginning, middle, and end; or, in other words, the exordium or introduction, the narration or proposition, and the conclusion.  The exordium, or introduction, should be employed, not indeed with the formality of rhetoric, but with the ease of genuine politeness and benevolence, in conciliating favor and attention; the narration or proposition, in stating the business with clearness and precision; the conclusion, in confirming what has been premised, in making apologies where any are necessary, and in cordial expressions of respect, esteem, or affection.

Scrupulously adhere to the rules of grammar.  Select and apply all your words with a strict regard to their proper signification, and whenever you have any doubts respecting the correctness or propriety of them, consult a dictionary or some good living authority.  Avoid, with particular care, all errors in orthography, in punctuation, and in the arrangement of words and phrases.

Dashes, underlinings, and interlineations, are much used by unskillful and careless writers, merely as substitutes for proper punctuation, and a correct, regular mode of expression.  The frequent recurrence of them greatly defaces a letter, and is equally inconsistent with neatness of appearance and regularity of composition.  All occasion for interlineations may usually be superseded by a little previous thought and attention.  Dashes are proper only when the sense evidently requires a greater pause than the common stops designate.  And in a well-constructed sentence, to underline a word is wholly useless, except on some very particular occasion we wish to attract peculiar attention to it, or to give it an uncommon degree of importance or emphasis.

Postscripts have a very awkward appearance, and they generally indicate thoughtlessness and inattention.  To make use of them in order to convey assurances of respect to the person to whom you write, or to those who are intimately connected with him, is particularly improper; it seems to imply that the sentiments you express are so slightly impressed upon your mind, that you had almost forgotten them or thought them scarcely worth mentioning.