Very early in a story, the author often shows the reader which category the story fits into. It is a mystery, science fiction, fantasy, romance, etc? This sounds easy, but is not always so.
Orson Scott Card, in his book about writing speculative fiction, tells about his first attempt at selling a story. The editor of the magazine, a famous science fiction author, rejected the story, explaining that the magazine only published science fiction. Card saw his story as science fiction. But eventually Card realized that anyone who did not know the background that he had worked out for his story would not recognize it as science fiction.
The steampunk sub-genre of speculative fiction sets stories historically, but with some key changes, either scientific or fantastic. If Andrew Jackson uses dragons in the Battle of New Orleans or if Elvis is kidnapped and sent back to confer with Mozart, the genre may be steampunk. But if the author waits until page 10 to introduce the dragons to Jackson, the reader may stop reading on page 8, since she was looking for a speculative fiction story, not historical fiction.
So, just stick a dragon in scene 1 of the Jackson story. Right? Maybe not. The author does have a story to tell and it might be nice to introduce Jackson in some other way first. But somehow, soon, the author needs to let the reader know early on that this is not just history.
One reason that Dean Koontz is fun to read is that one often cannot tell if she is reading a story about space aliens, wizards, a gifted hypnotist, a drug induced hallucination, or a simple mass murderer. Koontz often waits for many pages to establish the genre. Koontz can "get away with it" because many readers trust him since they have read his previous work.
So until one can command readers in the way that Koontz and King (and now Card), the author has another ball to keep in the air.