I have been an English teacher to teenagers and adults, and I know that cultural differences are the hardest things to teach, but among the most necessary. I certainly wish, for example, that someone had told me when I first went to France that when you go into a shop, even a supermarket, you should loudly Bonjour the whole shop and then bonjour the till person when you go to pay. If not they dislike you intensely. Although I suspect that in the west of France things are not quite thus. I have been asked for suggestions for cultural dos and donts for multinational young students of English, aside from the obvious - if you want two things you do not put two fingers up with the back of your hand facing the other person, and you do not look at or engage in conversation anybody else on the Tube. Anyway, this is what I came up with.
don't snap your fingers in a restaurant (I think only Russian oligarchs do this actually), don't take out your own food or drink if you are in a pub or a cafe, don't tap anyone on the shoulder or touch them in any way to get their attention (I saw a Brazilian do this, everyone avoided her after that and she never knew why), thank a bus driver, tip a hairdresser and a taxi driver but not a police officer, don't look people directly in the face on public transport, when you have finished your food and/or drink in a pub or cafe or restaurant you should order some more or leave, especially if it is crowded, respect the discretion line in a queue (eastern Europeans and Baltics don't do this), NEVER queue jump - people will not say anything but they will HATE you - if you are sitting on a bench or somewhere in a public place and someone else sits down you should move along a bit to give them space. French people don't do this. In the south of England only kiss your immediate family and very close friends, and then only on one cheek, in the north don't kiss anyone at all. If you are a man and you want to impress a woman tap her on the bottom with a rolled-up copy of the Racing Post and call her Princess.
I only made up one of those recommendations.