Hold the book
Imagine that together with your child you have invented a new Olympic sport - balancing with a book. Let the baby walk around the room, trying to hold it on his head and not drop it. He should not touch the book with his hands. Very soon the child will understand how important it is to move carefully, holding his head high.
Choose books of different formats so that he can understand which ones are easy to hold on his head and which ones are difficult. You can give the game the form of a competition between several children. One person plays the role of judge, while the others try to hold the books on their heads.
All children walk around the room at the same time, and the one who holds the book the longest without touching it wins. The winner becomes a judge and assigns a new format and weight of the book to the game participants.