The content of the book (qualitatively and quantitatively) is proportional to its favorable price. Néanmois, content remains fairly simplistic and popular: for example, we all know that a healthy lifestyle (Eat well, play sports, learn to rest ...) is needed to learn well! In addition, methods for learning are quite abstract, they rely heavily on the good will of the "appreneur", his desire to learn, to achieve its objectives ...
However, the method of "Conceptogram" (the best book in my opinion), very simple to apply (contrary to what has been said in another comment - which I can understand), can be very useful to quickly memorize a course a notion, talk, be a problem, take notes ...