Popularly referred to as the Feynman Technique, this technique involves explaining what you have learned to an imaginary student. Doing so provides active recall practice.
See also the discussion about How to Use the Feynman Technique.
Here is a longer explanation:
- How to Build a Memory Palace
- How to Remember Numbers with a Memory Palace
- Memory Palace Alternatives
- Natural Ways to Improve Memory
- Major System
- How to Memorize a Book
- Binary Number Memorization Systems
- Does Photographic Memory Exist?