When interviewers ask me, "How did you write your novels?" I usually cut short this line of questioning and reply, "From left to right." I realize that this is not a satisfactory answer, and that it can produce some astonishment in Arab countries and Israel.
Now I have time for a more detailed response. In the course of writing my first novel, I learned a few things. First, "inspiration" is a bad word that tricky authors use in order to seem artistically respectable. As the old adage goes, genius is ten percent inspiration and ninety percent perspriation. It is said that the French poet Lamartine often described the circumstances in which he had written one of his best poems: he claimed it had come to him fully formed in a sudden illumination, one night when he was wandering through the woods. After his death, somebody found in his study an impressive number of versions of that poem, which he had written and rewritten over the course of years.
Eco later talks about the preparatory work he did for his novels, including drawing a precise map of the monastary where In the Name of the Rose takes place, and sketching out the faces of the characters in The Island of the Day Before. (He also traveled to the South Pacific and spent days learning about the oceans and the night sky on one of those islands - obviously a research technique better suited to an author who has earned money from previous books.) For Foucalt's Pendulm he spent evening after evening wandering the museum where much of the action takes place and then walking Paris streets at night. The result is a verisimiltude that has earned the awe of legions of obsessive fans.
I love books rich in learning, observation and thought. I am extremely wary of books written quickly - Eco's quickest writing was two years, for In the Name of the Rose, since he could rely upon a lifetime of medieval research. (That's one reason I've never been even remotely interested in participating in NaNoWriMo, although dear friends have convinced me that it has its place.) Do you think you can tell the difference between a novel written on the fly and one that took its author years to plough through? Do you have a preference?