Imitate or follow someone's example, as in Harriet took a leaf out of her mother's book and began to keep track of how much money she was spending on food. This idiom alludes to tearing a page from a book. [c. 1800]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.