All ranks are capitalized in the body of your letter, as well as positions. If you have to go on to another page, make sure that you are putting more than just the signature block or just the courtesy copy area on that next page. The closing of this letter is kind of tricky. Your rank is not written in all capitals, and may be written out completely or abbreviated. Finally, when you sign your letter, do so in black ink.
Dark blue is also acceptable, but is highly discouraged.
If you have an attachment listing, then that list is placed three lines below the signature block and the courtesy copy listing three lines below that. When giving one of the copies to the person stated on the courtesy copy list, make sure to highlight their title within the list. In summary, remember to always print on both sides of the piece of paper if your letter takes up more than one side. It looks more professional and saves on wasted paper. The Tongue and Quill is an adequate reference that may help in some cases, but is not specific enough in many other areas.