One of the most essential ingredients to successful mathematical understanding is your ability to teach.
Say, a friend of you is having a torturous time understanding a formula or solving a problem. Don’t hesitate to approach him and give a short lecture on the concepts required.
Teaching may not sound like a serious business-unless you actually get on your feet to teach them. You will realize that you yourself were extremely vulnerable to certain concepts and will have a hard time re-studying them.
Moreover, the mentee might come up with some nice questions that you alone would not have thought of for a decade. In this way, the mentor-mentee can have a collaborative benefit.
After a successful lecture session, you will surprisingly realize that some concepts that were previously bouncing here and there eventually had solidified and aligned with themselves.