Depends where you are going.  Accents vary a lot from one part of the UK to the other. 

If you are going to use the trains, learn to order your tickets online, it is sometimes cheaper, you can pick up your rail tickets at the departing station from a ticket machine. The more in advance you can puchase tickets, generally, the cheaper they are.  You can really get ripped off on the trains if you do not know what you are doing.  National Express buses are good, but Megabus is usually much cheaper. 

Read up about Oyster Cards and London Underground, and try and book places like Madam Toussauds and London Eye online to save money.  If you are going to enjoy the nightlife, you can get VIP entry to many clubs by registering online, this will mean you can jump the very long queues to go in, and it does not cost any more.  Tiger Tiger in Leicester Square is a good night club and restaurant.  Very big. (there are Tiger Tiger clubs in many large cities).

If you wish to stay somewhere cheap, try the Backpackers Hostel in Picadilly Circus.  It is right in the middle of London, so travelling to the tourist places will be cheaper than if you stay outside of the area.

Remember, any problems, you can always ask a policeman, they are there to help you. 

Don't forget to visit Wales to see the most beautiful beaches and the greenest landscape in the world, not to mention the medieval castles that are dotted all over the country. 

Not much of a post on skills, but I hope it helps you enjoy your stay here a little more than you otherwise would have.

I'd recomend to search for videos on youtube about people from that country so you can listen and practice their accent.

You can improve your skills better in the UK :)

Bad news, just heard that Picadilly Backpackers hostel I mentioned is now closed!

Oddi, it is so useful information, thank you!