Vintage advice

"To put one's thoughts in a letter neatly and correctly is possible for anyone. To write fluently and gracefully is the result of training. To touch the heart of the reader, to make him chuckle, to make words paint pictures that transport another to distant scenes — these are gifts. But we can all express ourselves kindly, naturally, and in good taste. Our written words are permanent witnesses of our character. We can try to have the tone of our letters agreeable and appropriate. If one takes time to write he can make the letter an expression of his best self."
— By Edna Ingalls, co-author of "How to write letters for all occasions"

In my collection of writing books, I came across "How to Write Letters for all Occasions" by Alexander L. Sheff and Edna Ingalls (with revisions by Mary S. Allen), published in 1942.

It's divided into two sections: Business Letters and Social Letters. I found the Social Letters section quite interesting, especially the part on writing letters of condolence, which always seem difficult to pen.

Here is an example, from the book, of "a brief note of sympathy."

My Dear Susan,

Please accept my sincere sympathy for you in your sorrow.

Fondly,
Mary Walter

For "a longer not of sympathy":

Dear Susan,

The news of your sorrow has just reached me. I think I can realize your loss because I know how empty my world seemed when I heard of the passing of your mother. It will be very hard for all of us who knew her well to carry on without her, but we can be glad it was our privilege to have come in contact as long as we did with such a very lovely person. I shall always remember her kindness and cleverness.

Very sincerely,
Martha

The book has hundreds of sample letters on topics such as "Letters That Ask For Payment" and "Notes of Congratulations." It is still useful, some 67 years after it was first published.