Knowing the clients learning style/knowledge base. By the point of getting into the complexities of any project I have spent time with the client building rapport, instilling confidence, and really digging in on my end to understand both what the client knows from experience, and how they learn. With this information I can really get into details of a project and help the client understand what is being conveyed the way that they learn and can internalize the information. Generic or broad stroke information leads to more questions being unanswered and time wasted that could be spent on other aspects of the project. Its serving the client and the return on it serves the project and myself/team.
Use an analogy with which the audience is familiar. If you cannot, perhaps YOU do not fully grasp the concepts. For example, Authentication and access concepts can use the analogy of the plane ticket. Your ticket gets you through security (authentication). However, you only have access to a specific plane/fight. Even there, you have different 'rights' than the pilot or the flight crew. And you have 'rights' (access to s specific seat. It is the same once you log into your (or the cloud) network. You only have access to specific applications and data. The ticket analogy simplifies the concepts of authentication and authorization.