On the first day of class, create an environment that is conducive to how you want the classroom to function.
Move around the classroom so students do not become comfortable using their phones under their desks.
If students feel comfortable coming to teachers when they're lost, overwhelmed, or upset, they are less likely to perform poorly.
Students will grow tired of the class if it involves the same activities week to week. Be sure incorporate different ways of presenting information.
Ensure that all the tasks you assign can provide the student with small bits of information at one time. Dividing the lesson in chunks, you're less likely to overwhelm the student.
If the class is talking loudly ask for silence then wait 5 seconds to ensure all talking has stopped, thus ensuring all students will hear your next instructions and putting an end to the disruptive talking.