Ray Bradbury explained his model of creative writing at various times throughout his long and glorious career. He explained it at the greatest length in his non-fiction book Zen in the Art of Writing. This quotation sums up several key principles he explains in that lovely little book. Creative artists should not work primarily with their rational minds. If they plan, and try to reach some intentional creative goal, the result is stiff and artificial. They should instead work with several qualities which eventually unify: their senses, emotions, subconscious or intuition, and craft.
Bradbury believed in soaking up sense impressions. You can see this in stories like "The Pedestrian," where people go out walking at night, just to feel the air, or in Clarisse in Fahrenheit 451, who took joy in the feel of rain. These sense impressions should make you feel, first in your body and then in your emotions. In his aforementioned book on writing, Bradbury praises "zest" and "gusto." Writers should feel things intensely, and write quickly, so the words flow straight from the subconscious like a dream or vision. This is not without craft. That's where the reference to zen comes in. In zen, you might practice something a thousand times so it comes out without thinking the final time; Bradbury saw fiction the same way. He went through a period where he wrote a story a week, and he read voraciously. Extensive reading and writing let his passions flow into his stories without conscious planning.