Factors one should bear in mind while planning letters?

To whom to be address, subject, reference and the matter in brief.

Your address in top right hand corner with the date under it. Under the date (but on the left hand side) but the recepient address aswell as any reference number. Start with "Dear sir/madam" or "to whom it may concern" or if you know the name "Dear John". A paragraph every 8 or 10 lines or if the letter is only 10 lines long then put a paragraph at the half way point. End with "Yours sincerely" or "Yours faithfully" or "Many thanks".