What are the four English Language skills a teacher is supposed to develop in learners?

Basic four skills required to be developed in learners of English language are:

1. Speaking

2. Listening

3. Reading

4. Writing

To use some "older" words as a "supplement" to Anayat's answer:

Diction

Vocabulary

Comprehension

Grammar

The4 traditional  language skills: Listening,speaking,reading and writing.Modern studies consider CULTURE as the fifth language skill which is supposed to be developed in language teaching.