Simple children’s stories can be helpful for those who do not have a vast vocabulary and need to learn all grammatical constructions. Popular novels with profound vocabulary are suitable for people with medium and high levels of knowledge; from there, you will learn a lot of new words. Where to start and what to choose then?
You should take the English proficiency test to correctly categorise yourself as a reader. If your level is below the Pre-Intermediate, then read some simplified texts. Then, continue reading adapted literature. Remember an important detail: some publishers oversimplify texts, so a text at your level may sometimes seem very easy. In this case, buy a book at a more challenging level and increase the number of pages daily.