After the first manual, you may consider studying a second one, but then you should change strategy. An appropriate strategy for adults is to read what they usually read in their native language. If you are a philosopher, read books about philosophy, if you are a scientist, read books about science. Stick to what motivates you most. Later, you will discover that words can be divided into three great areas: 1) Language of science, documentaries, and media; 2) Language of prose; 3) Colloquial language (comic strips, etc.). These areas certainly overlap, but only to a certain degree. So even if you understand 99 percent of the words.
