I rely on a lot of archaeological research in writing my books. I'll take something like the following bit of information about the Hohokam:
"[T]he command area group—that is, farmers along a distribution canal who must coordinate and cooperate to irrigate using the same canal . . . was the primary level of organization and one that dealt directly with farmers. It was the task group that worked cooperatively to construct, maintain, and repair the common distribution canal. Ethnographic case studies also suggest that a task group maintained the section of the main canal in its area and, in situations such as repairing a headgate, the group worked as a unit. This was also the level in which water was allocated to individual farmers and required labor contributions were tracked."
[Source: Archaeology Southwest ASW 21(4), "Hohokam Archaeology of the Phoenix Basin."]
Then I imagine how these task groups would actually work with real people, and I let various characters play in my head for a while until scenes and plots start to coalesce.
There were hundreds of miles of these canals in the Phoenix area long before the first Europeans stepped foot in the valley. Many of them were so well engineered that modern canals follow the same course.
I had my mother teach me to read when I was four, and I've never stopped. Now I can play with words all day long... it's the best job in the world.