Pay attention to his process:
1. He read the text out loud (to make sense of it)
2. He underlined all the key words that help him understand the message
3. He took handwritten notes
4. In his notes, he explained to himself what he understood
5. He condensed his notes into ONE sentence, which is the main idea.
Questions worth asking yourself:
1. Do I take notes in English as I listen to /read/watch smth?
2. Can I take notes in English?
3. Do I use the words from the text (or from my head) to craft the main idea or the summary?
4. Do I read out loud?
5. Do I practice explaining things to myself?