How to learn any language?

Some time ago I came across a very interesting website by a Swiss amateur linguist François Micheloud. He presents an interesting table for those people who want to learn a foreign language, but don't know from which one to start (or which should be the next). François compares difficulty, popularity, transparency, the number of countries speaking the language etc. For instance he rates Russian to be the easiest languages among the "languages usually considered as hard".