• If you know the person's name:

     Dear Ms/Miss/Mrs/Mr/Dr + surname 

• Ending/complementary close: Yours sincerely is also British. Americans tend to reverse the order and write Sincerely yours.

When I worked in England, I was told that to write Sincerely without the Yours was very bad form. Now, of course, Sincerely is a common and acceptable close for American business letters. - ego4u.com 

• Mrs, Miss or Ms?
  Mrs – to address a married woman
  Miss – to address an unmarried woman (rarely used now)
  Ms – to address a woman whose marital status you don't know; also used to address an unmarried woman 
• The abbreviations Mr, Mrs etc. are usually written - without full stops (Mr) in British English and - with full stops (Mr.) in American English.

• If you don’t know the name of the recipient…
  
  Yours faithfully is British usage. It is used when the recipient is not addressed by name, as in a letter with a “Dear Sir” salutation. I have never seen it in correspondence between Americans. That’s not to say it won’t catch on. I’ve come across letter-writing guides on the web that imply that it is standard American usage.
  
  Yours truly is the American equivalent of “yours faithfully” that I was taught by my American business teachers. When I begin a letter “Dear Sir,” I close it with “Yours truly.”- .dailywritingtips.com

- Yours faithfully (to unknown person on business)
- Yours truly (to slight acquaintance)
- Yours very truly (ceremonious but cordial)
- Yours sincerely (in invitations a. friendly but not intimate letters)