Lady Elizabeth Anson knows a thing or two about etiquette. After all, she is royalty.
As Queen Elizabeth's first cousin by birth, and a party planner by trade, she is organizing a diplomatic reception the night before Prince William's wedding at the Mandarin Oriental Hotel.
It is almost a welcome party, hosted by the queen and to be attended by 60 crowned heads of state.
As a royal, Lady Anson knows the do's and don'ts for Kate and Will's big day.
"The dress code is a day dress or a suit or a coat and a dress and a hat. The men are in morning coat or uniform or national dress."
After the service, 650 guests have been invited back to Buckingham Palace. So what happens at the reception?
"The first that will happen when you arrive - there will be trays of drinks," says Lady Anson. "The best thing you can do is have a handbag on a chain or on a strap [so] you've got a hand for your champagne flute and you've got a hand to take your canapé."
Canapés or hors d'oeuvres will be served. Lady Anson says there's no need to hold back in front of the queen, however do make sure you don't have a mouth full if her majesty addresses you.
"If the queen is talking to you, you will find that the butlers do not come up with trays of canapés to you because it puts you in a difficult position," says Lady Anson.
And when greeting the queen?
Guests should also watch their body language. When first lady Michelle Obama greeted the queen with a hand on her back in 2009, she didn't seem to mind, but others should be more distant.
"I would shake her hand and I would probably kiss her and I would curtsy to her," says Lady Anson.
Apart from that: don't be late, don't tweet or update your Facebook status. And, of course, don't drink too much!
"That is royal etiquette," says Lady Anson.
But remember to have fun. "This is just a big family wedding isn't it?" laughs the queen's cousin.