People who have taken this exam seem to have a lot of problems with it for two main reasons. First, the exam covers a wide range of material. It is therefore essential to take your time studying and make sure that you prepare for all of the exam objectives.
The other thing that trips people up about this exam is that while most network administrators are used to performing configuration tasks, application infrastructure planning is something of a different animal. You have to understand how to configure the low-level infrastructures that various types of applications use, but you also need to understand how the configuration changes that you make could potentially impact the application itself and the end user experience.