Add more vampires (even if your vampire story is about vampires vampiring, add more).
Dragons being snuggly in the bones of those who came to rob them. Add that too. Key ingredient.
Your book does not have to have heroes or superheroes or Lawful or Neutral or Chaotic Good folk. In fact, try one without! Everyone can be evil!
If you MUST (read: desire on any level) have heroes, consider having them perish. Horribly. And the villain then goes to a spa. Relaxing!
Evergreen topics: Mermaids. Dryads. Monsters. Ghosts. Witches. Smooching. Falling in love.
Using necromancy to provide the energy necessary to finish your book is not cheating, it is technique.
Best of luck to you! Unless your hero wins in your book and then best of luck but with a sad tone in my wish!