If you study people, and when you see someone interesting, think, "Hey! She'd be a great character!"
You text yourself a great line that occurred to you while you were out running errands.
Watch a television show and think to yourself that you could've written it better.
Mentally rewrite sentences in a book you are reading, to make it - to your mind - read better.
You always have a story going on in your head. You may not necessarily be writing it, but there's one always going.
You have "everyday" pajamas and "formal" pajamas to wear while writing.