I bought the Exam Ref book written by Chris Sorensen. Link   

I watched the edX course videos and read the book twice before taking the exam.  I did not do the exercises in the book. The book is good but it is for preparing for the exam not for teaching beginners.

I think if you passed the 70-778 Power BI exam, you can easily pass this one.  Most of us BI developers started our careers before Power BI gained widespread popularity so we know Power Pivot/ the Excel Data model well.  You need to know the following topics to successfully pass the exam:

1. Basic DAX
2. Advanced Power Query
3. Excel visualization types
4. Understanding basic M code
5. Everything else from the skills measured list

This exam is recommended for BI developers and others who have never taken an MCP exam before and would like to start with an easy one.