The Data Driven Pages (DDP) has some powerful abilities for authoring map books, based on an Index Layer.
Unfortunately, the tools for the creation of this Index layer are not detailed enough and requires a lot of try & error.
I've created a document that ease the process of calculating the DDP Grid Index.
It enables you to pre-calculate the necessary parameters for the Index tool.
The document explains how to create an Index that fits perfectly to the desired Map scale, Page size and the Coordinates grid.
This is done using an Excel worksheet embedded in the document.
Good luck and happy indexing,