Curiosity, Not Virtuosity
Sometimes we fiddle and fuss with our prose but neglect the larger gyres of story. Other times the big plot arcs drive the writing. What is the thing that most reliably keeps the reader reading, in the moment? Curiosity. Whether it’s about what will happen next or the unpacking of some minor mystery in the present, curiosity drives readers forward far more that beautiful prose.
In the creature's narrative in Book II of Frankenstein, a new character, Safie, is introduced, largely as a vector to explain the monster's learning of spoken and written language. Who she is and why she can't communicate with the other characters, who clearly know her, is a mystery tantalizing enough to keep the reader's attention despite multiple implausible plot twists.
PROMPT
Ask yourself every chapter (or section, or page, or paragraph—depending on the scale of your work) what does the reader want to find out, now? If there's not a clear answer, go back and inject some mystery into the preceding scenes. In subsequent sections, fulfill some of this curiosity — but only some. Save some for later. Leave your reader yearning to know and understand more, and you will keep them turning the pages.