Proof read it carefully and then get someone else to proof read it. Typos are the kiss of death in cover letters and resumes.

You should take John Doe's recommendations and the forms you found on-line and try a draft for us to review. I'm sure you'll get blasted by somebody on here, but so what?

Keep it short. Use plain language.

EDIT: I didn't see jloman's comment before I posted this. Those are all great recommendations.

Do a draft and let us see it. We'll be gentle.