Explain it to a 12 year old: helps us to remove any jargon that might be hiding what we dont understand. use simple words. Where we struggle is a sign that we need to understand better.
Reflect, refine and simplify: go back to source material and try to understand the bits we struggled to explain in step 2
Organize and review: Test your explanation in the real world - run it by someone else
This can also help us when someone is trying to explain somehting to us. Asking questions on the bits we dont understand: if they are unable to explain it could be a a sign they don't understand it fully.
References
The Science of Rapid Skill Acquisition: Advanced Methods to Learn, Remember, and Master New Skills, Information, and Abilities - Peter Hollins