Although the test mainly focuses on the Graphic User Interface (GUI) of CME, it is still important to know how to enable the GUI and have a basic understanding of the concepts and protocols involved in the processing of calls and the characteristics of the different audio codecs available. Also, understanding QoS queuing algorithms is highly recommended.
The best preparation is a hands-on approach with CUCM, CME, and Unity. Some of the main objectives are related to your being able to create and modify users, phones, and lines. If you do not have access to these applications, I recommend you at least map out the different menus and understand what can be done within each of these menus.
As important as it is to know how to create phones or users, it is also important to understand the steps required to troubleshoot problems that may arise on the system in a systematic way. Cisco has defined an 8-step troubleshooting method that is worth looking at.