Of the utmost importance is that your own English be as perfect as possible, as well as your pronunciation of English words. Schools in other countries, for example do not wish their students to be encumbered with a poor English accent, thus if you do have a pronounced accent, your first work will be in getting rid of the accent. Take enunciation classes in order to accomplish this, or even Drama classes may be of help.
Because you wish to teach your students correctly, begin to set up your curriculum in your own mind. For instance how will you teach idiomatic phrases, or why English is useful for puns whereas most other languages do not have puns? The class work for puns usually entails a lot of laughter as the students report back on the best puns they could make with the advanced language studies they've already accomplished.
Colloquialisms should not be passed on to your students either, as you may teach them something that will not be used where they need to speak and understand English. Teaching listening techniques, so that they can actually understand what's being said, in spite of it being in English is difficult to impart too, yet it's a skill that is highly prized.
If you are going to teach English for a specific business, make sure that you understand the depth of any phrase that will be used in English, and why it will come handy for your students to have this knowledge, and how to actually use it. Will you be a ''total immersion'' instructor, or not? This means will you be demanding that all questions from your students be accomplished in English only? Depending on where you are teaching, this may be useful or may backfire on the instructor when no one wishes to ask any questions.
Do you believe in ''theme-based'' lessons? This means will you have a ''parts of the body day'' or a ''going to the seashore'' day? This kind of lesson can take a lot of preparation on your part with perhaps audiovisuals, or at least a drawing ability. If it were a history day, would you ask that your students dress in costumes, or perhaps yourself?
The use of crossword puzzles is a teaching tool that just about everyone likes. You can find crossword puzzles on a myriad of subjects, and in different degrees of difficulty as well.
Foods and holidays blend together well, for one lesson. You may even wish to bring in a representational food, to show your classroom what is eaten during a particular holiday. Pictures of foods are relatively easy to find, and you should use those often.