Are you a certified teacher in your country of citizenship & have teaching experience? If not, you must have it. Despite the ads touting jobs for native speakers - "no university degree necessary" - that's not true. Only fly-by-night schools will take those without degrees in English, Linguistics, Applied Linguistics, or related fields. Some countries require masters degree + TEFL certification + experience to apply for employment visa.
You MUST have teaching experience & at least a bachelors degree, in addition to TEFL certification to get a halfway decent job & the appropriate employment visa.
And teaching in a classroom full of language learners is nothing like the textbooks say, and you need experience no textbook can teach. Believe me - Been There, Done That. Criminy, even teaching in public schools in places like the US, where so many schools are loaded with immigrants who cannot (some will not) speak English is nothing like trying to teach abroad.