"Minute Meditations on the Mysteries of the Rosary" -- By Rev. Thomas M. Feeley
I found this book to be a wonderful help to focus on while praying the Rosary. If you are like me, you can't stay focused on prayer and meditation, and your mind just keeps jumping to all the things you need to do.
This book has been a great help to me.
Another good book to use while praying the Rosary is:
"Rosary of Praise" -- By Larry and Connie London
This is a good book to read when praying the Rosary with young children.
Both are excellent for young and old!