In somebody's good books means in favour with them at the moment. Stay in somebody's good books.
The moment is the point, since the position is temporary and easily lost. The bad books are the other half of the pair and are far easier to get into.
1phrasein somebody's good booksIn favour with somebody at the moment.
“Bringing the coffee kept him in somebody's good books all week.”
in somebody's good books is a phrase.
Practised in Idioms