Learning strategies are an important part of developing autonomy.
Example
A learner keeps a small notebook in their pocket and records interesting new language when they hear it, then researches it later using online reference material they have been shown.
In the classroom
There are a wide range of strategies available to learners. A teacher's responsibility is to expose learners to as many as possible, give them the opportunity to experiment, and help them identify what works.
Further links:
https://www.teachingenglish.org.uk/article/making-listening-authentic-experience
https://www.teachingenglish.org.uk/article/remembering-vocabulary
https://www.teachingenglish.org.uk/article/seven-steps-vocabulary-learning
https://www.teachingenglish.org.uk/article/lizzie-pinard-fostering-learner-autonomy