Today, set yourself up to journal the entire day tomorrow. That means having a pen and paper ready right when you wake up to record any thoughts or dreams. And continuing on through the day not missing any detail, conversation, thoughts, memories. This is based on a prompt in The Writer's Idea Book by Jack Heffron. He suggests "don't let more than an hour pass without writing."
He also writes "whatever you do, don't stop." If your day gets too busy, jot down words instead of notes. A few days later, or a week later take these notes and write a fictional character experiencing your day or expand your notes into a memoir piece. Now get back to work!
The Writing Nag