Reading a lot of books does not mean reading bad books. Someone can read broadly and selectively. To do so takes some research and discernment, and it also takes a sort of predetermination to read certain categories of books.
To that end, consider these four categories of books that you should read. The list is not comprehensive, but I hope it provides a good start for creating a personal criteria for books to read.
1. Books that encourage you towards something good
A primary purpose of reading is to become a better person. The best books inform, excite, and motivate you towards some good end. It could be as simple as learning more about the history of baseball. Yet such a book should ethically relay history and excite virtue in you. Find books like this in whatever genre you read books in.
2. Books that deepen your understanding of an important topic
If you agree with an argument, you probably do not need to read another book that simply reinforces what you already believe. Instead, find a book that goes beyond what you already know about a topic. Then you can deepen your knowledge about an argument, idea, concept or whatever it is. This will develop an intellectual virtue in you without letting your mind lay fallow for too long.
3. Books that you disagree with but still will read sympathetically
Only reading books that you already agree with is a recipe for confirmation bias. Besides, you may actually be wrong and need to correct your way of thinking. Reading books that you disagree with can do that. But it is not just reading such books. It is doing so sympathetically, by attempting to understand what the author argues, why the author may argue in such a way, and what it all means.
Even if you end up disagreeing still, you will actually know better why you hold to a belief than you did before—if you read sympathetically.
4. Books that excite your imagination and make you wonder
Make sure to read biographies, fiction, and any work that can engage your imagination (which could be a scientific study). Our imaginations form a key grid through which we view the world. Regularly experiencing awe will make you more interested in the world, a more interesting person, and more balanced person.
These four categories may help you figure out which books to read. Now, this list is not exhaustive. More could be added. Which ones would you add?