My first draft of book 6 started with a problem. It's easy to fix, since the Narrator can just impart the necessary information, but I thought I'd talk about these issues in general. It's expectation vs. reality. In this case, it comes from the fact that so far, many of my DbC novels are actually named after a subplot, a running joke, or a theme. They aren't actually named for the books primary plot. For instance, DbC 2 is subtitled The Wrath of Con. The game occurring during this book takes place during a convention, and the idea of a convention keeps coming up over and over throughout the book, but the book is in no way about conventions. In the case of book 6, the book is named after the alias of a character and his plot, which doesn't appear until chapter 13. However you learned the alias and the goal of his plan in the last book, so all I really need to do is remind (or inform) the reader of those facts in the first chapter or two. This way, the reader will know they are waiting for the plan to emerge instead of staring at the title in puzzlement, and then reading a chapter, then checking the title, shrugging, and reading another chapter, etc.
Dan Wells ran into a similar issue with I Am Not a Serial Killer. The fact that the book had a supernatural element isn't obvious right away, and readers had trouble with the sudden change in tone when the supernatural aspects emerged later. Dan solved it just as easily as I am in DbC 6. He had the first person narrator tell you about the supernatural aspect early on, even though his character didn't know yet. Since it was a 1st person narrator speaking in the past tense, the reader just assumes the narrator is relating the story after he discovered the truth.
Other expectations take more work (and it also depends on how you define expectation). We know from the Treason of Isengard that Tolkien knew very early in the writing process that Frodo wouldn't be able to throw the ring into the Crack of Doom, and Tolkien lays the groundwork for this from the beginning. Bilbo has difficulty giving up the ring, of course, but Frodo actually fails to throw the ring into a completely mundane fireplace at the beginning of the book. Right there, he sets out the expectation, if subconsciously. If Frodo can't throw the ring into a fire that can't hurt it, how is he going to must the will to actually destroy it at the end? And of course, we have the betrayal of Boromir, the growing power of the ring, and many other forms of foreshadowing throughout the book.
Another technique you'll see a lot, especially in movies and TV, is using the edits to direct the viewer's attention to a hidden bad guy. Pay attention, upon rewatching a mystery or a story with a hidden foe, and see how many times the main characters refer to the unknown bad guy, and then the show cuts immediately to the actual villain. You don't usually notice this, but it's slowly laying the groundwork in your brain so that when the villain is revealed, the reveal seems more inevitable.
Another example comes from a review of the original Ravenloft adventure in Dragon Magazine. While I didn't agree with the review, this one point stuck with me as a writer ever since. The reviewer criticized the challenges and traps of the adventure, saying that they drew attention away from the primary antagonist rather than pulling attention back to him and underscoring his menace. Writing Excuses had similar advice last weeks with subplots, advising against subplots that distracted from the primary plot as opposed to enriching the overall story. In the case of the mostly unseen antagonist, try to use foes, challenges, and threats who's nature resonates with the villain. Vampire stories might have stories where darkness, loss of control, and weakness are constant themes and challenges, even when the big bad guy isn't actually in the picture.
The hard part can be identifying these expectations. Possibly the easiest solution is just to have someone, not you, read the book and tell you what they see. Obviously, my Writers' Group told me that the title of the new book was strange enough that not knowing its relevance distracted them from the story. Howard Tayler will often have us read the first part of a Schlock book and ask us what promises he's made, just to see if he's missed any.
This issue of expectation, and fulfilling your promises, is critical to professional writing. It's one of the easiest things to get wrong, and when you don't nail it, it leaves the work feeling hollow and incomplete. This is slightly next level stuff here, but it's a next level you must hit if you're ever to write professionally.