Explaining it to somebody

Explain the topic out loud to a person, or to an empty room, without notes. The point where your voice slows or hedges is precisely the point you do not understand, and you will find it in seconds — far faster than by rereading.

This also happens to be the skill being examined in vivas, interviews and most of professional life. Studying this way and preparing to explain your work are the same activity, done once.