The official line is always that there is no set protocol of behaviour when the meeting the Queen.
But royal etiquette is still likely to be a tricky business for US President Donald Trump during his high-profile and controversial state visit to the UK.
With the world’s media preparing to dissect Mr Trump’s manners and moves as he spends time with the monarch, here’s a guide to what the American billionaire needs to know.
1. The bow and the curtsy
The monarch’s official website explains: “There are no obligatory codes of behaviour when meeting the Queen or a member of the royal family, but many people wish to observe the traditional forms.
“For men this is a neck bow (from the head only) whilst women do a small curtsy.”
Last time, there was speculation that Mr Trump failed to bow to the Queen when he arrived at Windsor Castle for his brief visit last July.
Opinion among commentators was divided but it appeared as if the US leader actually gave an early nod as he stepped from his car, dipping his head slightly, before walking forwards to shake hands with the Queen on the dais.
First Lady Melania Trump did not curtsy.
Former royal aides have insisted that the Queen is relaxed about such things and understands some people do not feel comfortable doing so.
But Mrs Trump should perhaps bear in mind that royal women greet the Queen with a deep curtsy as a mark of respect.
The Queen is also once said to have remarked about the knees of Cherie Blair, who is married to former prime minister Tony Blair: “They stiffen but they do not curtsy.”
2. The handshake
Mr Trump has form for grabbing hands and holding on to them for an extended period of time.
The Queen is unlikely to accept any extreme hand-holding, and there appeared to be none on show last time.
The monarchy’s official website has some simple advice on the matter.
It declares of those who decide not to bow or curtsy: “Other people prefer simply to shake hands in the usual way.”
Mr Trump has been described as approaching a handshake like an arm wrestle, in which he clasps the hand and pulls sharply, leaving the recipient off-balance.
He yanked French President Emmanuel Macron’s hand at the Bastille Day celebration in July 2017, holding on to it for nearly 30 seconds.
At the White House in April 2018, he also led the French leader away from reporters after shaking his hand and keeping hold of it.
Prime Minister Theresa May also encountered Mr Trump’s unusual mode of dealing with foreign leaders.
They held hands as they walked along at the White House during their first meeting in January 2017.
Mrs May later said the US president was “actually being a gentleman”.
“We were about to walk down a ramp, and he said it might be a bit awkward,” she said.
3. Remember where the Queen is standing
Mr Trump’s biggest royal faux pas came when he was invited by the Queen to inspect the Guard of Honour.
As the Queen and the president walked across the lawn of the quadrangle to view the troops, the monarch appeared to gesture and point several times for him to move closer to the front line of soldiers.
Mr Trump moved slightly closer, but then stood still in front of the Queen, meaning the monarch had to navigate her way around him so they could walk side by side.
4. Your Majesty
On presentation to the Queen, the correct formal address is “Your Majesty” and subsequently “Ma’am”, pronounced with a short “a” as in “jam”.
Eyebrows have already been raised after the White House referred to the Queen as “Her Royal Majesty” in its announcement of the impending visit.
5. No touching
Buckingham Palace always courteously insists touching the Queen is not a breach of protocol.
But it is the generally accepted custom that you do not touch the monarch other than shaking hands if she puts out her hand to greet you in this way.
That means no hugs, air kisses – unless you are family – or arms around the back or shoulder unless you are firm friends.
The Queen is unlikely to take offence, although tactile behaviour is not encouraged.
Former Canadian cyclist Louis Garneau put his arm round the Queen in 2002 as his wife took a picture of them together while the monarch was touring Canada.
But the Queen appeared not to mind and smiled broadly for the camera.
In 1992, the then Australian premier Paul Keating was dubbed the “Lizard of Oz” after cameras caught him giving the Queen a helping hand at Canberra’s Parliament House by touching her back.
Mr Trump should perhaps not try to emulate the rapport the Queen has with former US president Barack Obama and former first lady Michelle Obama.
Ahead of the G20 summit in 2009, the Queen and Mrs Obama acted like old friends when they put their arms around each other at Buckingham Palace.
In her memoir, Becoming, Mrs Obama said they had just agreed a long day wearing heels had left them with sore feet.
We were just “two tired ladies oppressed by our shoes”, she added.
6. State banquets
Mr Trump will be expected to follow Victorian-style table manners at the white-tie state banquet by talking to the person on his left for the first course – the Queen – and the person on his right – likely to be a senior royal – for the main course, following the rule that you keep changing for each course.
Formula One champion Lewis Hamilton revealed that the Queen once gave him a lesson in the etiquette over lunch.
“I was excited and started to talk to her but she said, pointing to my left, ‘No, you speak that way first and I’ll speak this way and then I’ll come back to you’,” Hamilton revealed.
7. Start outside and work your way in
This is the golden rule for negotiating the cutlery in the Buckingham Palace Ballroom.
Napkins must go on a guest’s lap and be placed on the chair if the guest has to leave the table during the meal. They only go on the table at the end of the meal.
Nineteen stations are set up around the table each manned by four staff – a page, footman, under butler and a wine butler – who use a traffic light system to co-ordinate the serving of courses.
8. Don’t fall asleep
The Duke of Edinburgh once dozed off during a state banquet in Seoul in 1999.
Seated next to South Korea’s president, Kim Dae-jung, he closed his eyes and nodded off briefly during a lengthy speech by the Queen.
9. No selfies
The Queen has occasionally accidentally photo-bombed the odd selfie, but asking the monarch for a selfie is a definite no-no.
She once said she found it strange to be greeted by a sea of mobile phones, telling then-US ambassador Matthew Barzun she missed eye contact.
The Queen’s second son, the Duke of York, has admitted he does not mind selfies, posing for his own first royal one in the palace in 2015.
Mrs Trump posted her own Happy New Year selfie this year, but is unlikely to be able to post one featuring the Queen.