If doubtful whether to end with “yours faithfully”, or “yours truly”, or “your most truly”, &c. (there are at least a dozen varieties, before you reach “yours affectionately”), refer to your correspondent’s last letter, and make your winding-up at least as friendly as his: in fact, even if a shade more friendly, it will do no harm!
A Postscript is a very useful invention: but it is not meant (as so many ladies suppose) to contain the real gist of the letter: it serves rather to throw into the shade any little matter we do not wish to make a fuss about. For example, your friend had promised to execute a commission for you in town, but forgot it, thereby putting you to great inconvenience: and he now writes to apologize for his negligence. It would be cruel, and needlessly crushing, to make it the main subject of your reply. How much more gracefully it comes in thus! “P.S. Don’t distress yourself any more about having omitted that little matter in town. I wo’n’t deny that it did put my plans out a little, at the time: but it’s all right now. I often forget things, myself: and ‘those, who live in glass-houses, mustn’t throw stones’, you know!”
When you take your letters to the Post, carry them in your hand. If you put them in your pocket you will take a long country-walk (I speak from experience), passing the Post-Office twice, going and returning, and, when you get home, will find them still in your pocket.