Stand to welcome her
When the queen enters the room, you are required to stand up to welcome her. Some people bow in front of the queen but that is not mandatory. A man should just bow his head a little from his neck; whereas, a lady may do a small curtsy. If the queen extends her gloved hand to you, you should touch her hand briefly; however, a firm handshake is strongly discouraged.
Address the queen as ‘Your Majesty’
Initially, you are required to address the queen as ‘Your Majesty’ but you may call her “Ma’am” afterwards. If there are other members of the Royal Family with the queen, you may call them ‘Your Royal Highness’ in the beginning and follow it up with ‘Sir’ or "Ma’am”.
It is highly recommended that you do not discuss private matters with the queen and choose appropriate topics of conversation. You may talk about something that you have read in the tabloid, for example.
Do not touch the queen
While meeting the queen, there is a no-touch rule that is observed by both the sides. Therefore, you must not touch the queen at any cost apart from when she extends her hand for a handshake. The President of the United States of America, Barack Obama, was touched on his shoulder by the queen in 2009 and that became a surprising story for many newspapers around the world.
Learn from others
It is advised that you do not make the mistakes made by people who have met the queen in the past. For example, saying ‘pleased to meet you’ is not advisable, as it is assumed that everyone is naturally pleased to meet the queen.