Learning = Minimizing Error
In a former life, I was an electrical engineer. My work involved finding the best ways for a transmitter to send information through noisy channels and then recover it with minimal errors at the receiver.
Since we were sending bits (1's and 0's), we wanted to minimize the bit error rate. And we wanted that error rate to be very low for a wide variety of commonly-encountered scenarios.
I can't help but see language acquisition in a similar light. I am fluent in English because I can transmit and receive information to and from other English speakers with a low error rate for a wide variety of commonly-encountered scenarios.
In engineering, one smart way to approach minimizing a system's error rate is to first find out what the most frequent mistakes are being caused by, and fix those first.
I think you see where this is going. Since I don't speak French, my "error rate" in French comprehension & communication is very high. But if I can find out the most commonly used words in French and learn those first, that should be the fastest way to fluency.
Still... what a monumental task to generate such a frequency-ordered vocabulary list! To assemble it properly you'd have to tabulate it over a wide survey of French media. I'm talking spoken and written sources encompassing newspapers, telephone calls, magazines, user manuals, weather bulletins, literature, plays, government hearings, fiction, non-fiction, interviews with athletes, interviews with businessmen, ...
My friends, to my GREAT DELIGHT I've discovered that someone has already done that work for us!
I can't believe it actually exists and the only reason I haven't purchased mine yet is because (a) I can't decide whether it'll be easier to use on kindle or paperback and (b) there's no pressing need to decide today since you get immediate access to the first 362 words by downloading the free kindle sample (done!).
We live in fantastic times.