Royal weddings are full of protocol but for guests at Prince William and Kate Middleton's big day how should the key players be spoken to?
The wedding reception will feature a traditional receiving line with the couple, Prince Charles and Kate's parents, Mr and Mrs Middleton.
Queen
Ma'am | mam to rhyme with Pam

Never speak unless spoken to. Aim for anything within the public realm and avoid anything private.
Did Your Majesty enjoy the wedding breakfast? GOOD
Who's looking after the corgis? BADPrinces & Princesses
His or her Royal Highness

Anyone who has a title should be addressed as "Your Royal Highness" for the first time, and subsequently "Sir" or "Ma'am" (to rhyme with Pam).
Clergy
Archbishop of Canterbury

If you are introduced to the Archbishop of Canterbury address him as "Your Grace" or "Archbishop", the Dean of Westminster is addressed simply as "Dean".
Source: Debretts