Whilst I agree with this in principle, IME it helps if you can say in (however basic it may be) French that you dont speak French but can they please ..... Also, when you approach someone, start with the greeting 'bonjour / bonsoir madame' or 'bonjour / bonsoir monsieur' (as the case may be) and on leaving end of with a 'merci et au revoir' (this - especially - includes waiters and shop assistants!). Using these little forms of politeness will help immensely and the Frenchman / woman is then quite likely to be willing to converse in English. It is the way they operate themselves and not greeting is considered extremely rude.
Just to assume that everyone speaks English and will be happy to discard their home language in their own country is in my books a little arrogant. I do the same in each country I travel to, but I find that in France the effect is really quite significant.