Rereading books helps children become fluent readers and recall words quickly without needing to spend time sounding out each word. More brain power can be used for understanding reading and reading with expression when books are read multiple times. The trick is to find those great books children want to read more than once.
Children should have a number of books they can read by themselves they find interesting enough to read again and again. My own children each have a cardboard magazine box filled with books they can and like to read. Usually I listen to my child read the book aloud at least once before we put it in the box. Make the book fun. Enjoy the story, laugh, look at the pictures, connect the story to an event or other book you've read, make guesses about what might happen next, talk about something new you learned if it's a non-fiction book ... etc.
Support your child's reading when necessary.
If a book has more than one in ten difficult words, read the book to the child. After the child has listened to the book a few times, it might become a book to read independently. Most reading experts agree: no more than 1 in 20 difficult words is Independent, no more than 1 in 10 difficult words is Instructional, and more than 1 in 10 difficult words is Frustration. A child may miss two or three words together, don't panic. You want to avoid too many starts and stops that break up the flow of reading. When there is a lot of stopping in a sentence, a reader can reread a sentence to get back into the flow.
Choose books your child likes. Continue adding books to the Collection of Books for Rereading. Ask your child to decide which books to take out when it starts getting full. Keep a book in the box as long as a child wants it, even if it seems too easy.
Set aside at least 20 minutes a day for reading. If you have more than one child, use the time your children are rereading from their collections to listen to one child read a new interesting book.
Books can be read aloud or silently. Encourage your child to read to brother, sister, another parent, a grandparent, a friend, a relative or even a pet. Children love to share their favorite books.
Our family uses cardboard boxes

and labels them with each child's name. That way favorite books can be taken to any comfortable reading place in the house, in the car, or to Grandma's house.

Increase Fluency by Rereading Favorite Books