What makes a good book depends on the genre. Good novels will generally have strong characters, well developed plot lines, and a rich setting. Good nonfiction books will be clear, accurate, and engaging. These are the best books to read. Novels which have weak characters, no plot, or a bad message are generally not good books to read.
Furthermore, non-fiction books that contain inaccurate information or that are not well written or that do not engage with important ideas are not as good to read. What counts as good book or bad book cannot be made just by looking at the cover of a book, as the saying goes, so it is good to read all books and afterwards decide for yourself whether a book was good book or not, otherwise you are just going by what others say. It is possible that a book everyone says is bad will turn out to be good one for you.