You have to sort of suppress other complex thoughts when speaking about complex thoughts on the fly. Most of the time, consciously trying to simplify individual sentences about already-complex topics makes them easier to say without really harming the inherent complexity that ensues in the conversation.

Just don't worry about making mistakes, people will almost always give you the benefit of the doubt about what you mean or give you the opportunity to re-explain something or to take a pause to collect your thoughts.