Developing metacognitive awareness is an important part of helping learners become more effective and, importantly, more autonomous. If learners are conscious of how they learn then they can identify the most effective ways of doing so.
Example
The teacher asks the learners to keep a diary of their classes in which they can note what they liked and didn't like and why. They then discuss their ideas and develop individual and class action plans.
In the classroom
One of the most effective and easiest ways to develop metacognitive awareness is simply talking with learners about how they do things in the classroom, such as recording new words, reading a text, and laying out a page in their notebooks.
Further links:
https://www.teachingenglish.org.uk/article/learner-training-young-learners
https://www.teachingenglish.org.uk/article/learnenglish-teens-learner-diary