The right answer is: listen to the speaker's main points.
When you are listening to someone, a teacher in the classroom, for example, it is difficult later to remember everything the person said or understand the discourse that is being developed, one of the ways to achieve it is by focusing on the main points that the interlocutor is indicating and if possible to point them. Understanding the main points will give coherence to the speech and allow you to understand it and then remember.
I hope this information can help you.