There are not so many books about language learning, but this is the best one I found. Short, witty and precise, it tells you all the basics of language learning on your own. Barry Farber speaks over  25 languages, among them chinese, russian and finnish.

I read this book for the first time when I was 16, and it took me 9 years to fully develop its ideas.

You can buy it from Amazon.com for about 12$, which is the best price I found,   or if you live in Europe as I do, from Amazon.co.uk.