A lot of English people complain that the French are rude, unfriendly, and unhelpful. A lot of our French friends and neighbours ask us why the English are so rude and ill mannered.
A paradox, perhaps. The explanation is fairly simple: the French are extremely formal and polite, and regard the absence of the formalities as insulting. Here's an example of how deep it goes. I was sitting in a beachside cafe, when there was a roar of engines and three bikers pulled up. They got off their bikes, and walked to the cafe, their chains clanking, their big boots clomping, their tattoos catching the light, their leathers creaking, and their long greasy hair flopping around their heads. I became just a little tense, they were big, ugly blokes, two of them with facial scars. The waiter was a wispy 18 year old student earning a bit of money in the summer. These huge bikers went to a table, and the waiter bustled up and said 'Bonjour, messieurs'. Each of the bikers meekly said 'Bonjour, monsieur' back, and sat down to order their coffees and a citron presse.
As this politeness - and effectively expression of respect - dates back to the Revolution, and you are in their country, it must be up to you to adapt to their ways. Fortunately, this is easy, even if you do not speak the language. All you have to do is use a few key words appropriately and you will find that not only is everyone helpful and friendly, but a lot more speak some English than you might realise.
The first rule is that you must always say Bonjour before any other communication. Even close friends will say it when they meet before they kiss each other. Even the checkout cashier in the supermarket will say it to all the customers. If you go into a shop, the other customers will say it to you. Not to say it is extremely rude.
In the supermarket in the tourist season, I have often seen a cashier being terribly helpful to all the customers, and then say Bonjour to an English tourist who just stares blankly at her. She feels insulted, becomes sullen, doesn't understand a word of English, and so the tourist has problems in dealing with paying and everything else. The next tourist says Bonjour back, and she speaks enough English for a sensible conversation.
The second rule is that you must nearly always address people as Monsieur or Madame, as in Bonjour Madame. All French people do so except for very close friends, or children. We are Monsieur Paul and Madame Averil, to our neighbours and everyone in the village - because our surnames are unpronounceable.
The third rule is always to say Si’l vous plait (please) and merci (thank you) as appropriate. If you can only point to what you want, still say s'il vous plait, and merci when you get it. I know this sounds like teaching children, but people who don't speak French forget such simple essentials when confronted with a non English speaker.
Another useful word is pardon (sorry), to be used whenever you don't understand. Finally, always say au revoir Monsieur / Madame when you leave.
So, less than a dozen syllables are all you need to be welcomed, if you use them all the time. Any phrase book or dictionary will be very helpful as well.
The key is that not saying Bonjour when you meet someone is the equivalent of starting a conversation by saying 'Oi, pigface' to an English person.
The reason the French are so pervasively, perhaps excessively, polite may not be remembered by most of them, but after 200 years it is well embedded. Before the Revolution, the aristocrats treated ordinary people like animals, but demanded total deference from them. In the first phase of the Revolution, everyone became equal (egalite and fraternite) and was called Citoyen (citizen). Even the king was called Citoyen Capet at his trial.
After the excesses of the Terror, things changed again, and instead of everyone being equally low, everyone became equally significant. Thus all people were addressed as My Lord (Mon Sieur) or My Lady (Ma Dame), and every request was accompanied by If it pleases you (S'iI vous plait) and so on. Not to do so was to declare yourself opposed to the Revolution, and this was not a good thing to be. Now, such behaviour does not involve prison, if you're lucky!, but it is seen as offensive. And if someone is rude to you, you will be rude to them. Easy, isn't it. However, none of this applies to Paris, where almost everybody is always rude, just like London. Still be polite, but don't expect everyone to be nice back.