It's all about input and output. On the weekends and afternoons during the week, I take drives and soak up all the sensory information I can, and then on weekday mornings and evenings, I translate those raw-material sensory experiences into fictional lives. My sensory real-world experiences, feelings, perceptions, etc, are what breathe life into the characters. When my characters walk through the woods, for example, I can feel the tree bark beneath the fingers of people that don't exist. I can feel the soft -- almost bouncy -- forest floor beneath the feet of people that do not exist.
Writing is such an amazing re-living; I don't understand why everyone isn't a novelist. :)