This was supposedly given to US troops stationed in the UK:
http://www.hardscrabblefarm.com/ww2/britian.htm
It contains lots of trueisms about the British:
The British dislike bragging and showing off. American wages and American soldier’s pay are the highest in the world. When pay day comes it would be sound practice to learn to spend your money according to British standards. They consider you highly paid. They won’t think any better of you for throwing money around; they are more likely to feel that you haven’t learned the common-sense virtues of thrift.
The British Are Tough. Don’t be misled by the British tendency to be soft-spoken and polite. If they need to be, they can be plenty tough. The English language didn’t spread across the oceans and over the mountains and jungles and swamps of the world because these people were panty-waists.
And some tips on the language barrier:
Some Hints on British Words. British slang is something you will have to pick up for yourself. But even apart from slang, there are many words which have different meanings from the way we use them and many common objects have different names. For instance, instead of railroads, automobiles, and radios, the British will talk about railways, motor-cars, and wireless sets. A railroad tie is a sleeper. A freight car is a goods wagon. A man who works on the roadbed is a navvy. A streetcar is a tram. Automobile lingo is just as different. A light truck is a lorry. The top of a car is the hood. What we call the hood (of the engine) is a bonnet. The fenders are wings. A wrench is a spanner. Gas is petrol—if there is any.
Also includes a list of dos and don’ts