Reading books is a great way to be exposed to natural language in context. Not only do they help you notice language — structures — in real, contextualized use but they also expose you to meaningful vocabulary.
Jack Richards (2015:443,444) claims that adults may read for different purposes. The author lists some of them: for everyday activities, for learning about things, for life purposes, for leisure and pleasure, for study purposes and for work purposes.
Because of this, I decided to share the following link, which contains short stories in case you do not have much time to read entire books. Remember that the more you read, the better!
Richards, J. (2015). Key issues in language teaching. Cambridge, UK: CUP.