Is the heading suitable?
Have you followed the conventions for the date?
Have you filled in the references?
Is there a subject line?
Do salutation and complimentary close match?
Have you mentioned the enclosures?
Have you signed the letter?
Have you done a spelling check?
Is your use of language appropriate for the relationship that you have with the addressee?
Is the language business-like and to the point?
Is your information concise?
Does the letter leave sufficient room for the recipient to formulate a reply without exerting undue pressure?
Have you shown the recipient the right degree of respect?
Has the content been logically and appropriately organised?
Have you left proper margins?
Does the layout look pleasing?
Is the type of paper you used suitable?