Native Spanish speaker from Argentina, just created an account to answer this. First, you should probably decide what regional variant to learn, and stick with it. There are subtle but noticeable differences in style, words and accent between, say, Mexican, Spanish and Argentine "Spanish". If you only want to practice reading, you could probably go for books of acknowledged writers (García Márquez, Vargas Llosa, Borges, etc). It depends very much on your preferences, you can search something related to your hobbies or your work. Hope this helps.