Prepare well for each lesson. Know exactly what you are going to do in class. Prepare a range of activities before the class and be ready to move on to another one if your first try doesn't work well.
Focus on the needs of your students and adapt your lessons appropriately. A class of doctors may need very different vocabulary than a class of high school students preparing for study abroad.
Give all classes ample opportunity to speak the language. At lower levels, this will often be in the form of drilling with students repeating pieces of language after you. At higher levels, give students more freedom to express their opinions and ideas.
Conduct your classes entirely in English. It may be tempting to resort to the students' native language at times, but this can be counter-productive and unnecessary if you have prepared well for the lesson. Instead, modify your language to the level of your students.
Conduct communicative, task-based activities in every class. Give students opportunities to use the language in a meaningful way in class.
Incorporate language games into your lessons for all levels of students. Integrate appropriate language-based games into your lessons, not just as a reward for good work or a treat on a Friday afternoon. They provide motivation as well as an enjoyable reason to use the English language in class.
Guide students through appropriate activities to discover the meaning of new language themselves. Your students will remember it better than if you simply tell them the meaning of grammar or vocabulary.
Have your students speak to each other in pairs and groups to maximize the amount of time students spend speaking English. After setting up the activity, observe, give help when necessary, and take note of your students' language strengths and weaknesses.
Give students feedback on their use of English at the end of activities. It is important to avoid interrupting activities while the students are working unless absolutely necessary. In addition, emphasize language that students have used correctly and give the class the opportunity to correct mistakes themselves.