1. imitate someone else's behaviour, especially to gain an advantage
Professional
Social
he/she is very successful, I should really take a leaf out of his/her book
'Leaves' refer to the pages in a book. If you take a leaf out of someone's book it means to imitate, copy or emulate someone in a particular way. If you take a leaf out of someone's book you behave in the way that they do. Usually, this expression refers to copying someone's good or beneficial behaviour. "You should take a leaf out of his book and start getting up earlier in the mornings." (Note: Although 'you should take a page out of his book' technically means the same thing, it is not an established idiom and so the received meaning is not the same.)