Turn baby's favorite book upside down and start to read aloud.
Purposely pick up your baby’s favorite book upside down and start to read. Quickly “discover” your mistake and correct it. This will send the message that books have a right way to open them up. Soon you’ll notice your child adjusting a book in his lap in order to have the front cover right-side up.
For toddlers, make a big, silly deal about how you can't read the book because all the words and pictures are upside down. Ask your toddler if he can help "fix" your problem.