Give a red dragon kobolds who keep the watch on its borders, dwarf slaves laboring under the whips of dragonborn, drakes as guards -- which is fine for the DM, except that you may not want it to go on. One campaign against the dragon; another against a lich; a third against a golem-infested ruin.
A novel, of course, centers around a single menace, however multi-facetted (or else has a source of unity that drives it farther from the game). So does a story cycle, though perhaps more episodic. It helps to have a land where the perils are the same sort. All monsters composed of parts of other beasts, or humans: centaurs, chimera, manticores, mermaids. Or all undead, and perhaps even there limited to necromancer-raised skeletons or necromancer-trapped ghosts.
The thing is, in a D&D game, the first option takes a cleric's ability to turn undead and renders it moot. The second turns it into a game-breaking power. Now, while keeping the players happy with their characters' ability to contribute is not crucial in a novel, the readers will wonder why on earth you have superfluous characters, if you do. (Then, you could do a story with the cleric alone, much more easily. . . . )