Behind the grandeur and grandeur of their lifestyle lies a strict set of protocols that they must adhere to. Members of the royal family interact with the public but are forbidden from taking selfies. They are only allowed to shake hands and greet each other. However, in recent times, Catherine has sometimes deviated from this rule, as evidenced by her willingness to pose for a selfie in a recent video at the Fox Club Nursery, suggesting that the selfie ban should be reconsidered.

Autograph giving is not allowed due to the risk of forgery and fraudulent use of royal signatures. At the 2023 Chelsea Flower Show, when a child asked for her autograph, Catherine replied: "My name is Catherine; I'm not allowed to write my signature. It's just one of those rules." However, she made amends by drawing a flower for the disappointed girl.

Catherine is not allowed to go to bed when she has free time because it is considered impolite and shows improper upbringing. According to long-standing custom, all members of the family must stop eating after the King has finished eating, which requires the princess to adjust her eating speed accordingly.

Royal women's makeup should be natural and simple, and nail decorations should not be used. Catherine's nails should be carefully maintained but are usually nude or pale in color. Notably, during the first Easter without Queen Elizabeth II, she was seen wearing bright red nail polish for the first time since marrying William in 2011.

The princess is expected to wear conservative, understated outfits in muted colours. Overly revealing outfits, such as short skirts and low-cut necklines, are strictly prohibited. In line with the royal family's commitment to animal welfare, outfits made from natural fur are also banned. While adherence to the dress code can vary, it is generally accepted that royal ladies are encouraged to wear tights at formal events and not remove their outerwear in public.

While Catherine enjoys grocery shopping and visiting shops, she cannot do so unaccompanied. Security regulations stipulate that she must always be accompanied by a security guard when leaving the palace. Years ago, the late Queen Elizabeth II banned family members from playing the competitive board game Monopoly. Prince Andrew has previously commented that the game had become too competitive, saying, “We’re not allowed to play Monopoly at home, it’s become too brutal.”

The royal family is notoriously reluctant to show affection in public, rarely kissing or holding hands in public. Some observers may attribute this to royal protocol, while others maintain a professional demeanor during public engagements, as they are representatives of the monarchy. The royal family receives many gifts from well-wishers during official engagements and abroad. However, there are restrictions on what they can accept. They can accept small items such as flowers or a reasonable amount of consumer goods, but cannot accept gifts worth more than £150 from members of the public.