Why write a vampire novel? Because you can be ultra creative with this icon of modern culture. Not only can you create an underworld populated by the undead, you can then unleash them on an unsuspecting real world. The vampire has bitten every popular genre in literature, film and television. They broke out of the horror genre long ago, but that's not to say there isn't a place in horror for the vampire. However, the vampire is not constrained; as a writer, you can unleash him/her into new territory.
If you have a passion for science fiction, what about designing you own vampire? Would your vampire be humanoid or a totally alien creature from another planet, for whom sunlight is deadly and human blood is like nectar. Think about a futuristic novel, one where the human race is fighting a loosing battle not to become merely cattle for alien vampire invaders. Has your human protagonist been transported into the future only to discover humankind are being farmed? How would they feel watching humankind being consumed as food, do they find a way to return to the present or are they trapped in a nightmare future? Does your protagonist save the world or end up as a blood smoothie in a vampire health food bar?
Try writing a scene, not necessarily the opening chapter. Write it in the first person, giving the emotional reaction of your human protagonist when he sees humans being farmed, like cattle, for consumption. The possibilities for exploring man's consumption of the earth with that of the aliens' consumption of humans are almost limitless. Would other earthly species thrive? Has global warming created an environment prefect for the aliens? This will give you a starting point for deciding the themes for your novel. If you prefer, write a short story or a poem, the starting point is to get something down on paper or on the screen.
See our writing course schedule for the word limit and how to get feedback on this exercise. Remember, let your imagination run amok. The future is yours and it's filled with aillien vampires.