When I sent mine:
-standard business format
-my tone was friendly but succinct
-mention your grades or don't but definitely send transcripts when there's a change (anything to get them looking at your file again!)
-mention what you're doing (work, volunteer, research)
-when I finished my degree (Master's) I mentioned it along w/ final GPA even though I had sent transcripts
-sent mine to the admissions committee or office of admissions (sometimes to the assoc dean of admissions if there was any relationship)
I have no significant "inside" knowledge, this is just what I did and I got in.
Good Luck!