When the initial little impulse comes it just tends to come. I wake up in the middle of the night, or I'll be swimming in the pool with my kids and just think, "Can't forget that one." Then there's the more organized side of the brain, which is when I choose to work on them. I've learned through a bunch of mentors how to demarcate the different times for your writing process. I keep multiple projects going at once and there's a time when no matter what you're doing, you have to stop and write it because it's coming.