Start teaching using only conversation. Avoid translating into the students' first language. Instead, teach through context. Use gestures, photos and props to associate new words with their meaning. Allow your students to get used to the sound of the words and how to pronounce them on their own. For example, start the first class by saying and having the students repeat "Hello, my name is ..." without writing this down in English. Students may get distracted by the letters and try to read and pronounce them as they would in their own language. Accompany this with a handshake or wave and by pointing to yourself or using another gesture.
Introduce the alphabet. A great challenge for language learners is the vast discrepancy between the spelling and pronunciation of English. Even if they speak a language that uses the same alphabet as English, the letters will be pronounced differently. Be clear and thorough in teaching the alphabet, as students will need to learn how to spell by pronouncing the letters as they are used in English. As the class progresses, include ongoing assessment of their spelling and listening skills regarding writing by doing dictations in class or playing games such as hangman.
Research the common problems associated with speakers of your students' first language. If you are teaching in a foreign country, most of your students will have the same first language (or "L1"). Misconceptions and common mistakes and confusion are especially evident with beginning students and it is easier to catch the problems before they become habits. The book "Learner English" by Michael Swan includes chapters on common problems faced by language learners of several L1s. Being able to anticipate such problems and learn how to combat them can help make you a more effective teacher.