With any closing, you'll usually include a comma directly after it. If it's something emphatic, you can use an exclamation point instead. For instance, you would write your closing like one of the following examples: Love, Stay safe, Affectionately, Stay as you are! Leave a blank line between the closing and your signature. Since you're sending it to a friend, just your first name is usually fine for a signature. You can also use a nickname if the person usually calls you by it. Postscripts, indicated by a "P.S" after your signature, were originally a way to include something in a handwritten letter that you'd forgotten. You can't just go back and add something because there's no space. However, they're even used in typed letters and emails nowadays, as a way to add a little fact or fun directive. For example, you might write, "P.S. You'd better write me back goofball!" if your friend isn't great about sending mail back. Alternatively, you could try, "P.S. I hope this letter gets there before I do!"

Summary:
Use a comma after your closing. Sign your name after skipping a line. Add a postscript if you forgot something in your letter.