Do you know enough grammar?
If you are a native English speaker, you will have no difficulty speaking English fluently. You should also be able to write reasonably well. But it is still possible that you don’t know anything about English grammar. Speaking English is one thing. Teaching it is an altogether different thing. If you are a teacher, you should know grammar.
Many native English speakers don’t understand what adjectives or adverbs are. They haven’t even heard about participles or modifiers. Of course, they can use these words in a sentence, but if you are planning to become an English teacher, you also need to know what these words do in a sentence. You must also be able to explain these things to your students. In other words, you should have a decent understanding of grammar rules. Aspiring ESL teachers who haven’t learned grammar at school or university must acquire a professional qualification in EFL/ESL before they start teaching.
Buy a good grammar book and learn the rules. These days you can plenty of ESL learning and teaching materials online. So it really isn’t difficult if you are serious about it.
Are you willing to teach people of all age groups?
Unlike a regular school or university teacher, ESL teachers have to teach people of all age groups. Sometimes you may be teaching very young kids. Sometimes you may be teaching folks much older than you. If you are not exactly comfortable with this situation, you should consider teaching at a regular school where they only admit children of a certain age. Most ESL schools, on the other hand, accept all students – young and old.
Are you willing to work in another country?
Some people are; some aren’t. ESL teaching jobs can be found everywhere. So even if you are not willing to leave your country, you should be able to find some opportunities. But if you are willing to travel, you have much better opportunities. Of course, working in another country comes with its fair share of surprises and disappointments. If you are not good at adapting to new circumstances you may find this difficult.