TEFL is an umbrella term for teaching English to students of any age whose first language is not English. TESL refers to teaching students who will be using English instead of their native language after moving to an English-speaking country.
As a quality, English teachers should have outstanding vocabularies, with a firm grasp of word pronunciation and spelling and the ability to effortlessly break words down phonetically. They are expected to have a strong command of grammar and sentence structure rules, with a systematic and consistent approach to enforcing them.
Grammar guidelines often require a repetitious approach, with a teaching style that balances classroom participation against the needs of individual students if they fall behind.