The best way to learn and speak fluent French (and any other language by the way) is immersion: go and live in a country where people speak French for at least 3 months, you will learn the stuff that isn’t taught in classrooms.

This is useless if you go to a place where you can find many people who speak your language. I have a friend who went to London to learn English. He came back with the same level of English than before, just because he spent every evening with French people.