The complexity of languagevocabulary and sentence structureis appropriate to the age range of intended audience. If a subject has complex terminology, a glossary is included. Even though the language is expository, it is of the same high quality as narrative. Clear, interesting, organized language renders complicated subjects comprehensible to readers. After reading, a reader usually wants to find out more about the subject.
Readers intuit how to write exposition from reading good non-fiction.
Careful study, research, and preparation are evident. An appropriate amount of information for particular readership is given. If a book is for young readers, a comprehensive overview provides the main ideas. The arrangement of format of text and illustrations attracts the reader's attention, clarifies concepts, makes information easy to remember, and motivates the reader to continue reading. If the author has bias, it is clearly stated.