Many tips can be given but the first, and probably the most useful, is this: be a pro. What does that involve? Many things. In our field, there are two important areas: knowledge of the subject, that is, the language; and knowledge of the procedures; that is, how to teach. With regards to language, you may want to ask yourself the following: Is my command of the language satisfactory? If I haven´t already, can I pass international exams at high levels? (e.g. Michigan Higher, CAE or CPE). In the many years I have taught at all type of institutions and levels, I have found that teachers tend to oversee and regret this important area. The result is that, in the majority of cases, the teachers´ command of the language they want to teach is really poor. If you want to teach English, then, learn it first. But learn it well, and then keep on learning more.
The knowledge of the procedures of teaching is much more than attending “workshops” organized with a commercial objective in mind or going to weekend conferences or taking certificate/ diploma level courses. Going through TEFL topics shallowly, in 90-minute talks or one-month-twice-a-week classes, is not the way to become a professional: more effort is needed. Happily, there are opportunities everywhere. Universities have now opened programmes for teachers who do not have a degree. The quality varies, but the market is full of these so we can choose. It depends on us.