Most of the time the best way to learn something is the top-down approach: from the more general to the more specific.
The left-to-right approach, which leads to the general view through lots of specifics, usually works better if it complements the top-down approach.
Why is the top-down approach better? We are used to thinking linearly; one stream of thought at a time - better not waste it on useless specifics.
If we can maintain more streams/flows of though at the same time, and the data we learn can be parallelized, then the left-to-right approach becomes more efficient and basically forms the subconscious aspect of top-down learning.
How to learn efficiently when approaching a subject matter?
First, we have to establish a context; we have to feed the subconscious with massive amounts of data. When reading books, this is achieved by listing through the book and reading random sentences.
When the context is established, the conscious mind now has something to work with. We can proceed to build a framework; a general idea that can hold the more specific ideas - we browse parts of the book.
When we have the context, the general idea and the more specific ideas, we have to connect it all together. This is achieved by reading the book from beginning to end, to fill in the holes in understanding.
After the mental structure, the understanding is complete, spend some to contemplate the conclusions of your understanding, as related to yourself and your goals.
This method can be applied to various other learning methods, not just learning from books.
For example, to learn a language, it is best at first to be exposed to massive amounts of material in that language. This is necessary to establish the context; to feel the ebb and flow of language.
The grammar of a language is the general idea; you have to feel it and know some of it. Later comes the gradual learning of specifics: words, ideas, phrases.
In the last phase, you realize you can successfully maintain your streams of thought in that language.
Books, as linear constructions, do not permit too much non-linear structure. (It would require too much bothersome redundancy.)
To compensate for this, the reader can read the book not only from beginning to end but in various ways, and the author too has too make sure that the literary structures exhibit a certain sense of coherency when read in a non-linear fashion.
The most common flaw when reading a book is simply reading it from the beginning to end; this doesn't do much justice to the book as a whole.
Inflexible part recognition (when reading separately as letters, words, sentences, lines etc. and not as a continuous flow) and other forms of linearity (when reading flows only one way with no other movement) too can inhibit the learning process.
Forcing oneself emphasizes only the "this is too hard" and "I don't know" aspects of learning which are very counterproductive.
Understanding comes by allowing.