It is an important aspect of language but an extremely complex one, as decisions about how to say things depend on understanding exactly what is right for the context and the culture.
Example
It may be appropriate to say ‘hold on a minute, will you?' in one context and ‘Could you wait a moment, please?' in another.
In the classroom
Focusing on inappropriate forms of language and delivery first is a good way to raise awareness of this area. For example, learners can identify inappropriate in language in video material such as comedy programmes, match language to contexts where it can be used, and discuss what is appropriate in their own cultures. In general, it is exposure to a range of authentic material that will help students develop their understanding of appropriacy.
Further links:
https://www.teachingenglish.org.uk/article/teaching-exam-based-writing-skills