You could start by asking what the students have already studied and ask to see books they have used to get an idea of the level they are at. You could spend the first lesson actually using this material to see how well they cope with it. This will help you plan the next step.
The basics of EFL teaching cover grammar, vocabulary, useful set phrases, pronunciation, speaking, listening, reading and writing. You can do a number of different activities from these areas to introduce variety into your classes. It’s not necessary to always cover all these areas but they serve as a useful guideline. Students have different needs and reasons for learning English, so spend some time finding out what they intend to use English for. You can then plan your lessons accordingly.
When teaching think about correcting mistakes, this is an important part of the learning process. Think about:
Which errors to correct
Who corrects? You or the student?
When to correct: immediately the mistake is made or will you note down errors to go over at the end of the lesson?
I’m sure you’ll enjoy your new career, it can be very fulfilling and interesting.