How to start your letter (Task 1 general training)?

In IELTS (GT), when writing to someone you don’t know (such as when writing to a company), the question tells you to start your letter with:

Dear Sir or Madam,

Otherwise, when writing to a specific imaginary person (such as your neighbour, your boss, your colleague etc), the question tells you to start with:

Dear …………. ,

In that case, what to write after “Dear” depends on the relationship and on the culture.

For IELTS, we can assume the Australian or British culture would apply. Therefore:

To someone of similar status whom you have spoken with (e.g. a friend, neighbour, colleague, immediate supervisor or line manager), use their first name.
For example:
Dear John,
To someone who is above you in terms of relationship status (e.g. a teacher/instructor, a customer) or whom you haven’t met, use “Mr.” or “Ms.” + (surname), which shows more respect. For example:
   Dear Mr. Smith, (for a man) or
   Dear Ms. Brown, (for a woman) or
   Dear Mrs. Brown, (if you know that she’s married and she prefers ‘Mrs.’) or
   Dear Dr. Smith, (if he/she is a doctor)

Don’t address the person as “Sir” + (name) — unless the person has been knighted, in which case, “Sir” + (first name and/or surname).

Some famous people who have been knighted: