Don't expect too much from this book that the author would tell you how she learnt 16 languages. There is only one chapter about it. Actually, there is only half of a chapter about it because she even dedicated another half of the chapter talking about the differences between men and women when they learn languages...

Anyway, I think the key idea of how she mastered 16 languages is that she always tried to grasp the meaning of the words and the grammars by herself before she asked the help of a dictionary. She made her own glossary and formed her own understanding of the languages. In this way, learning languages is more motivated and more fun.

So the rule is forgetting about what the teachers and the textbooks told us about what we should do while learning language. Just find some ways we really like to use the language as often as possible.