What's the best way to learn speaking English?

I have been having a thing for the English language for as long as I can remember. When I was just 4 or 5 years old, in my kindergarten we had an English class every Wednesday.

I don't remember a lot about it, I can't even tell if we had an English mothertongue teacher, but I remember clearly that the first stage was learning color names, and the next step was learning the animal names.

So, summoning 2 years of English in kindergarten I was able to say "The pig is pink" and I found it very funny.

Later in 1989 I moved to a small town, where no English class was available until I was 12 y.o.

By that time I already tried to learn some English by myself, but I had an English dictionary which was no help when you don't know the grammar.

My mom had an LP by Michael Jackson (Bad) and on the back cover there were the lyrics of some (maybe all) of the songs. So I kept looking on the dictionary for the word "are", without being able to understand why Michael used it so often if it wasn't even on the dictionary!

He looked so cool, but he talked an out of fashion-ed way. Wow!

So when I was in midschool I was about 12 y.o. and had real English classes with an Italian teacher. Reading the English mothertongue mums living in Italy, I have to say my teacher was pretty good for being an Italian. Or maybe it was me that had no benchmark and no clue about American English and British English. Italian English teachers have an issue with AmE, for they believe the only "real" and "genuine" English is the one of the citizen of the Kingdom, thus driving the children born from American mothers mad, as they are repeatedly corrected by their Italian teachers for saying/writing "specialize" instead of "specialise"

That aside, although I am very fond of my first English teacher even if she was Italian, I have to say that later in the years I called my Californian English teacher a "mistress" and she was very surprised to be called so. My first teacher said that "Mrs." was the short form for "mistress", but forgot to mention that nowadays "mistress" is not a nice name to call someone.

Now, after two years of work I came in contact with foreigner people and the official language to be used (and the only one we barely know) is English. But funny enough, our resident engineer is German and speaks English the way I speak Spanish, by ear.

Sometimes it is harder to understand a broken English for someone who knows very well the language rather for some other brokenly English speaker. 

Anyway, in my plant nobody speaks English, so the words they learnt were brought in by this German engineer, who definitely has an issue with English, both spoken and written. (He's taking Italian classes, anyway). So in my plant, and there alone, we pronounce "turbine" in an unique way that won't be understood anywhere else in the world, I assume.

When I tried to correct this habit among my colleagues, I still had to convince the German engineer to switch to /turbIn/, and there I failed.

So, what's the best way to learn English? At school? On the field? I guess none of the above. I'd take private lessons if I only knew of somebody in the area available.