Here is what I do:
Day One: Give them the rules and expectations for the class (in English and Chinese) on a syllabus and tell them that they are required to have the syllabus with them each time they come to class. (Give a fair and reasonable but steady amount of homework and quizzes on syllabus. FOLLOW THE SYLLABUS EACH DAY IN CLASS. Give exact grade percentages on the syllabus and make sure that at least 85% of the grade you give them comes from their work or their behavior in class.) Give them assigned seats (quickly deals with the back row kids) and tell them that if they are not in that seat at the beginning of class they will be marked absent and get a 0 for the day. (In my classes I make a copy of the seating chart for every day of class. When students contribute to class, are on time and are prepared, they get two points. If only one of the above is true, they get one point. If none are true, they get zero points. I average these points and make this 15% of their final grade. (the other 85% coming from homework, quizzes and presentations.) I aloso tell them that each time they talk in class (constructively contributing to class or asking a questions, answering a question, they get a check. If they get have on average 5 checks a day - i will add 5% to their grade at the end of the class.
Day One continued: I smile and look nice - but REALLY lay down the law about what is expected in class. I have been working on my “teacher smile” - pleasant looking smile - but not overly friendly. DRESS UP! Wear a suit, tie, nice dress, good shoes - whatever makes you feel and look dressed up. This adds to your professionalism and authority in the class. I now dress like my mother on days that I teach. Not too stylish - but it DOES help give the students the image of TEACHER in the front of the class and makes me feel more professional. I usually dress up for the first two months and gradually get more casual - but even by the end of the year I wouldn’t be caught dead in jeans and a t-shirt in front of a class. (I think this is important to because I am a.)female, b.)young-looking, c.) fairly attractive - so students think that I am going to be really nice and a pushover. Dressing up and looking older/more professional helps get rid of these ideas.)
Other points to consider:
NEVER show them you are angry. If students are being really disruptive, go back to where they are. Look them in the eye and in a totally calm and level voice say, “You have two choices, you can leave now or you can choose to participate in class.” Stare them down until they answer you. If they are disruptive again, go back, look them in the eye and say, “You have made your choice for today - you need to leave. Now.” Stare them down (with a totally calm, cool look on your face) until they leave. Count to 5 if you have to - it sometimes helps steady the nerves. Eventually they will begin to behave in class - maybe. But you will have shown by not getting angry that you are not personally offended with their behavior and that it doesn’t really affect you. This makes it less fun for them.
Sometimes classes just suck. This probably has nothing to do with you. Maybe the students had a bad teacher before you, maybe they don’t like one another, maybe they hate their major, maybe there are too many different personalities in the class. I really think there is very little you can do about these kinds of classes. Just teach what is on your syllabus. It may be horrible and mind-numbing. I have a class like that right now and I dread it every Monday morning (Monday at 9am doesn’t help them or me much either). So I have them do excercises, I call on them instead of them raising their hands, and just grind through. More than 1/2 of them are going to fail themselves because of their tardiness/absence from class and lack of homework. That isn’t my problem - they knew the rules from day one and I remind them often - but at the end of the day - it is their choice to learn and engage in class.
Set up a signal in your class for when it is time for them to be quiet. For me - I stand in the front - say ok and raise my hand. This is the signal that I want to tell them something and they need to stop what they are doing and listen. I do the same thing each time, whether they are sitting at their desks or running around the room with a survey. It now takes about 10 sec for me to get their attention.
Finally - I think that it will be hard for you to get control of them at this stage of the game - BUT I would suggest trying seat assignments (you can base it on their grades - clustering bad students around good students in little square patterns) and having a “talk” with them about how you think things are going in class, changes you want to make and changes they might want to make. Start from square one if you can.