[Whistleblower]

However, before I mentioned there are two divides of language skills. It depends upon which perspective you are looking at.

Productive skills include:
Speaking and writing

Receptive skills include:
Listening and reading

I recommend that you read 'Learning Teaching' by Scrivener. It is the best book out there to help you improve your knowledge of teaching English to students. It also covers the skills of language learning and how to teach particular skills.