Don't give the queen a friendly hug and don't tweet from the church.
That's just the start of the advice being offered to those attending Britain's April 29 royal wedding.
St. James's Palace says the guest list is an eclectic mix of European royalty, military personnel, charity workers, diplomats and friends of Prince William and fiancée Kate Middleton. Some invitees will have been born into families that teach children to curtsey as soon as they can walk, but others may need a bit of help navigating the etiquette and protocol that such an important day demands.
Anyone who is invited to the royal wedding will be given detailed instructions on how and when to arrive at Westminster Abbey, where the wedding is being held.
The first rule: Don't be late.
"The queen should be the very last person to arrive at the church before the bride and her attendants," said wedding planner and etiquette adviser Sarah Hayward. "At most weddings, guests are asked to arrive around 20 minutes before the ceremony but the royal wedding will obviously have several important guests and very high levels of security so give yourself plenty of time to get there."
Next, choose an outfit that blends in.
Women should wear a dress - not too short, not too skimpy and certainly not white. Most British women will complete the look with a hat or a fascinator - a small feathered or jewelled hairpiece attached to a clip or a comb.
"Never ever ever do anything to draw too much attention to yourself," says Hayward. "It's the day the bride shines."
Men in the armed forces should wear a military uniform. Male civilians are asked to wear either lounge suits - business suits by another name - or a morning suit, formal attire that includes a long jacket and a vest. A tophat should be carried, not worn, inside the church.
Couples should remember they will be seen together.
"Often you see a husband and wife who look like they are going to two different events," says William Hanson, an expert on protocol who gives lessons around the world on proper behaviour. "One person will be in something that looks like pajamas and the other is in black tie. You don't need to be colour coordinated but do think about how your outfits look together."
Guests may be asked by security to leave their cell phones outside the Abbey, but if they aren't, they need to make sure a ringing phone is not heard by millions during a service broadcast live around the world.
"The ultimate faux pas would be to have your mobile phone go off in the Abbey, even if you had God Save the Queen as your ringtone," Hayward said.
Tweeting or updating your Facebook status during the day is also bad manners.
"It's a private occasion and it would certainly be an abuse of the invitation to take photos or tweet during the ceremony or any point in the day," said Hanson.
After the morning ceremony at the Abbey, some 600 guests are invited to a reception at Buckingham Palace, where the food and drinks are sure to be amazing. Hanson advises guests to accept the offerings politely - but don't gobble, don't gulp - and for goodness sakes don't get drunk.
"Sip your drink, don't gulp it and always be aware how much alcohol you can tolerate," said Hanson. "Don't embarrass yourself (otherwise) for you can guarantee you will never be invited to this kind of wedding again."
Guests should also watch their body language. Michelle Obama put a friendly hand on Queen Elizabeth II's back during a visit in 2009. The queen didn't seem to mind - she even put her own arm around Mrs. Obama's waist - but guests at the royal wedding should be more distant.
"Never touch the queen. Never initiate conversation with her or any member of the royal family. They will do all that," said Hayward.
British citizens or members of the Commonwealth countries would traditionally curtsey or bow to the queen and her family. The royal family no longer insists that people do so, but most people still do bow or curtsey when meeting the queen.
"Nothing too theatrical," said Hanson. "Men should just bow from the neck - a nod really - and women should do a slight dip with their right foot behind their left foot."
After the wedding ceremony, Middleton will be a full member of the royal family and should be treated in the same manner as her in-laws.
Etiquette rules are designed to make social occasions flow more smoothly and to put everyone at ease. Experts say if a guest is unsure about how to behave, they should just take cues from the people around them.
"Remember that the royal family are masters of coordinating this kind of event," said Hanson. "They know how to deal with people from all sorts of backgrounds, from all around the world, and they know how to help people do the right thing."