Neil Gaiman, the author of Coraline, The Graveyard Book and many more, addresses the all important question...Where do you get ideas for your books? He used to respond:

"From the Idea-of-the-Month Club," or "From a little ideas shop in Bognor Regis," or "From a dusty old book full of ideas in my basement." But now, when talking to children he honestly says, you get ideas from daydreaming. You get ideas from being bored. You get ideas all the time. The only difference between writers and other people is we notice when we're doing it.

You get ideas when you ask yourself simple questions. The most important of the questions is just, What if...?

This article could be a great lead in to discussing the all important question with your students. Where do you get your ideas?

http://www.neilgaiman.com/p/Cool_Stuff/Essays/Essays_By_Neil/Where_do_you_get_your_ideas%3F