It takes a lot more than fluent in Mandarin and English to be a good Mandarin teacher, fine communication skills, patience, and good preparation is indispensable. It's an easy mistake to make for students to learn Mandarin as a second language to say it the same way they speak their native language, translating a sentence word by word in to Mandarin, without considering the different ways of expression or grammar. It really is not the end of the world when they do so, enough time and continuous correction must be given before we can expect them to adopt the "Mandarin way of thinking". Encouragement and sense of humor can also nourish their motivation. Pronunciation, grammar, vocabulary, sentence, culture and historical knowledge could be intersect with one another, stories and news can surely help to keep students interested in class. Family members, hobbies, and personal experiences are good topics to use when introducing new words or grammar, it is also a lot less stressful for them talking about things they are interested in when practicing.
Generally speaking, most of the students find the four tones of Pinyin dreadfully confusing. This is when phonics come in, slowly repeating the tones, initials, vowels over and over again until the students are familiar enough with the syllabus, and eventually being able to say them without struggling. And The same method could be applied on handling some challenging pronunciations like "q, c, ch, zh, sh".
One on one teaching gives great flexibility to teachers, teaching plans could be made individually according to the need of each student.