Harry Potter is often recommended. It is great for language learners because it is widely available and starts with relatively simple language and then increases in difficulty as the series progresses. The only difficulty is that there are quite a lot of words that belong to the fantasy world and are not used in real live English. There are seven books in the series. The 'His Dark Materials' series by Phillip Pullman is another good series that starts out easier and gradually becomes more difficult. The same problem exists as with Harry Potter, though. The story takes place in another world, similar to but not identical to ours; many of the words are invented for the story, or spellings of real English words are slightly altered. There are three books in the series. 'Where the Red Fern Grows' is a classic young adults book. It is written in simple language, but it's a good length. It's a standalone book. Mary Higgins Clark writes simple to follow mysteries for adults. They're easy to find, each of a good length and she has at least 30 books, so if you end up liking them there are plenty to choose from. The Outlander series by Diana Gabaldon is most popular with women, so it might not appeal to you, but the books are LONG, the language is pretty easy in the early books and there are many books in the series. And I can't think of the author's name, but there are is a series known as the Stephanie Plum books. They're comedy thrillers. Again, most popular with women, but I know some men do read them. Lots of books in the series, very easy language, and most people find them really funny.