One reason I am an illustrator is that it's easier for me to draw it than write it. Once my fourth grade teacher, Miss Pearl, assigned us to write reports about the journey of Marco Polo. When she saw that I was stymied, she encouraged me to illustrate it. My report turned into a picture book and I got an "A". Everyone loved my title page with Marco standing proudly on the prow of his ship, looking toward the distant, unknown world. One drawing could say all of these words and more!
Just this example shows how much I need to be into the story, its events, its people, their feeling and actions, and the places - as much as the author. And since writing is itself a visual art, imagine the advantage of sharing that process with Janice, including our travels through space and time, sketching and noting people, places and events.
Writing with Pictures by Uri Shulevitz introduced me to the magic of storyboards as the first step in illustrating a picture book. Using a large sheet of paper I draw a series of rectangles, one for each page of the book. Then I fill them with quick thumbnail sketches that tell the story.
The next step is to enlarge the sketches to book size, incorporating the text. During this process I collect pictures (photographs, drawings, paintings) and use models (Janice, myself, children in our neighborhood, horses in a local stable, historic sites, trees, creeks, and more). Then I refine my sketches by drawing on a light table. With a sketch taped to the glass top, I lay another sheet of paper over it and make a more detailed drawing on the lines I can see through the paper. This process goes on for many a sheet.
Eventually I take out a sheet of watercolor paper, place it on the light table over my latest drawing, and trace the lines with a pencil. Then I get out my brush and watercolors and PAINT...WHEW!

Partial storyboard from Young Wolf and Spirit Horse