The most important thing that you can do to prepare for this exam is to take the 70-341 exam first. That exam ensures that you have most of the basic skills you will need in order to pass this exam.
Once you have learned the basic skills required to deploy, configure, manage, and troubleshoot Exchange Server 2013, be sure to spend some time learning about deployment and coexistence. Although exam 70-341 touches on deployment and coexistence, this exam goes into those topics in a lot more detail. For example, you will need to know how to do cross forest coexistence deployments.
This exam also places a considerable amount of emphasis on compliance. Make sure that you know how to perform e-discovery and message records management. You should also know how to use the various Exchange Server 2013 features to implement compliance solutions such as ethical firewalls, transport rules, and message classifications.
Recommended Study Resources
Exchange Server 2013 and Exam 70-342 are both so new that there is a distinct lack of study resources available. Currently Microsoft does not offer any live classes or Microsoft press books.
There are currently no third party training books available for self study either. Even so, there is at least one generalized Exchange Server 2013 books available: Exchange Server 2013 Unleashed