First I would write the letter I WANT TO WRITE. Then, rewrite it, being polite and correct. THEN REWRITE it again, removing any "personal" type comments (this is one place "I" sentences don't work well...x

for example instead of saying," You need to know..." say something like, "It was suggested that you be informed of a situation that occurred..."

instead of saying ,"She accused me..." say something like, "This person implied that..."