A book picked from your own shelves can be a simple but thrilling way into finding about the interior life of a character. What was your character's favourite childhood book and how does that influence them or take up space in their imagination now? What is your character reading, if anything, at the moment? How does this book play in their mind as they go about their business and interact with the other characters? How can you use the physicality of a book – its feel, smell, condition – to evoke atmosphere and create a sense of possibility? How can you use the act of reading – its interiority – to affect the pace and mood of what you're writing?
Pick a picture or two and write the story of the book being chosen, found or given and read.
Go into your local library or second hand bookshop, pick out some books and imagine who held them last and why...