|Sir John, the Right Reverend, Your Majesties...|
Fans of Downton Abbey on the gogglebox faulted Maggie Smith for addressing a Duke as "Duke" - but that is how you address a Duke. It's only servants who call him "Your Grace".
To start from the top, when you first meet the Queen you call her "Your Majesty" - subsequently you call her "Ma'am", to rhyme with spam. For Prince Charles it's "Your Royal Highness" and "Sir".
Whatever you do, don't ask the titled person how you should address them. If you're not sure, discreetly ask someone else, or follow their lead. Admittedly, it doesn't help if the titled person is known to their intimates as "Bobo". In any walk of life, it doesn't do to call someone by a nickname if you aren't of their inner circle.
Anyone called Lord John Jones is the younger son of a Duke or Earl. Life peers are Lord Jones, or John Jones, not Lord John Jones.
A Knight is called Sir John Jones and is addressed as "Sir John"; his wife is "Lady Jones".
If you're going abroad, read one of those "Going to Syldavia on Business" type books, which should tell you if the Germans still call each other Fraulein Schmidt and Herr Braun when they've known each other for years.
If you're introduced from someone from the Far East, try and work out which is the family and which is the personal name. The Chinese put family names first, but they may switch to make it easier for you.
My friends Jen and Mrs Definitely talk about “grandfather” and “mother-in-law”, whereas I'd say “my grandfather” or “grandpa”. I call my mother-in-law by her first name, and refer to her as "Harry's mother".
Debretts have the full story – also in book form.