Please/thank you and sorry/you’re welcome (or my pleasure or no worries etc) are really important to use liberally - we say them all the time and find it rude if people don’t use them.
Most people are friendly, especially outside London, and it is not unusual for people to say “Hello” or “Good morning” when you pass in the street in many places (in London people will mostly ignore you unless there is a problem and then they will usually offer to help).
If you bump into someone or they bump into you, it is good manners to say “Sorry!”.
We hold the door open for people behind us, and if someone holds the door for you, it is usual to say “Thanks!”
On public transport, it is good manners to offer your seat to someone who is pregnant, has a small child or is elderly.
Queuing is really important here, it is extremely bad manners to jump a queue in the U.K.
There are manners associated with eating in restaurants etc but you probably don’t need to worry too much about that, as unless you are in a very formal setting, we are quite casual.
It is normal to call most people by their first name, rather than their title or surname unless in a very formal setting - however they introduce themselves is what you should call them (“Hi, I’m Mrs Smith” then call them Mrs Smith, or “Hi, I am Alexander, but you can call me Alex” etc).
Greetings could be either a simple hello, or a handshake, some people will kiss on one or both cheeks or hug as a greeting, depending on how close you are or how warm a person they are.
We are generally not very touchy-feely and like our personal space. Other Europeans and Americans tend to stand too close for our comfort and we back away!