Set up as per with your address and their address and date.
Your address (no personalisation) goes top right, tab across as needed.
ther address (inc personalisation) goes lower left.
date goes on same tab/start point as your address. leave 3 spaces to hand write date, but type month and year.
leave 3 lines for you to write in Sir/Ma'am.
I have the honour to inform you I am posted to [insert posting] as per [insert ref to posting order and date].
Who are you, where are you now, what do you do there.
any good stuff about you. ie skipper of the footy club
where you want to go
Yours faithfully (don't bother with that 'obeident servant' pish)
five lines blank for signature.
Make sure you phone your next unit and get the EXACT details of who you are writing to, including any post nominals.