OK, I am an American English professor. I would never recommend reading for "usefulness." That is a singularly Asian or Eastern concept.
I have an answer, but it is more philosophical rather than grammatical. The best way to improve your writing is to read good writing. One should not, however, seek out texts for their "usefulness" to you. Read what you like, anything that's interesting or entertaining. If you think of reading as a chore, a task, a challenge to be me met with hard work and concentration you are asking for trouble. Relax. If you are a reader you will be a better writer. Seek out well-known writers of fiction, newspapers, literary magazines that appeal to you. Enjoy good writing, and go and sin no more!