Instructions for American Servicemen in Britain is a fascinating and occasionally hilarious guide written for GIs headed to Britain—then half-ruined by war—in 1942. Subjects range from common-sense basics ("instead of railroads, automobiles, and radios, the British will talk about railways, motor-cars, and wireless") to subtle social pitfalls regarding race, sex and income. You can read it online for free; following are some choice excerpts.
The British don't know how to make a good cup of coffee. You don't know how to make a good cup of tea. It's an even swap.
The British are often more reserved in conduct than we. On a small crowded island where forty-five million people live, each man learns to guard his privacy carefully-and is equally careful not to invade another man's privacy.
If you are invited to eat with a family don't eat too much. Otherwise you may eat up their weekly rations.
The British are used to this [monetary] system and they like it, and all your arguments that the American decimal system is better won't convince them.
A British woman officer or non-commissioned officer can and often does give orders to a man private. The men obey smartly and know it is no shame. For British women have proven themselves in this war. They have died at the gun posts ... When you see a girl in khaki or air-force blue with a bit of ribbon on her tunic--remember she didn't get it for knitting more socks than anyone else in Ipswich.
The British have seen a good many Americans and they like Americans. They will like your frankness as long as it is friendly. They will expect you to be generous.
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.
The British have theaters and movies (which they call "cinemas") as we do. But the great place of recreation is the "pub."