The short answer is – as much as possible!

Most importantly and obviously, you need a good grasp of the English language itself, not just daily usage and vocabulary but at least basic grammar as well as spelling and punctuation.

An understanding of the roots of the language can help enormously.

An understanding of foreign language students is also an important aspect many potential teachers overlook. To be able to put yourself in the position of the learner, by understanding the student’s own language, or at least by appreciating the more difficult aspects of English, greatly enhances your readiness for teaching.

If you have an eye on a particular nationality of student you would like to teach, a basic grasp of their general culture will benefit you considerably.

Even with a formal qualification, your performance in a job interview is still the most important aspect of the hiring process for any language school.

If there is no minimum qualification requirement, the employer will have great expectations surrounding your personality and attitude.

Remember, teaching is the ultimate ‘people’ job – your ability to act with professional ease, patience and enthusiasm with any other people, is a highly-valued quality.

Any relevant work experience – private tuition, childcare, etc. will be looked upon favourably, and display your enthusiasm for this kind of career. Understanding and sympathy for your students, an appreciation of classroom dynamics, potential difficulties and strategies you have for dealing with this, again reveal aptitude for teaching.

Finally, think about pressures facing school and potential colleagues. As with any job you’re considering, the ability to help, a generally positive attitude, teamwork skills and the appropriate personality traits (in this case, being outgoing, approachable, professional but not intimidating) will help expose your suitability for TESL teaching.