Reviewing what you have learned and learning anew, you are fit to be a teacher.

Teaching well needs two habits that seem to pull in opposite directions. Going back over what you already know deepens it and reveals gaps you thought were closed, while learning something new keeps you humble and in touch with what it is like not to know. A teacher who only repeats grows stale, and one who only chases novelty never masters anything.

You do not need a classroom for this. If you guide anyone, a colleague, a child or a friend, revisit a basic you learned long ago, and also start something where you are a beginner. Both will improve how you explain things.