The tip for all exams is to study the exam topics that is listed on online for each exam. Then evaluate your understanding of them as you study. Cisco and other vendors don't care in the slightest if the Official Study Guide doesn't cover a topic fully (or at all) hell some tracks don't even have OCGs.
That's helpful, thank you, but where do I turn to actually study those topics? In other words, I grant you that it's important to have an authoritative list, and the OSGs may very well not, but where do I go to learn about the topics on the list, in depth?