Prevention is better than cure. Establish certain standards at the beginning of the semester by defining expectations in the course syllabus and reviewing those expectations on the first day of class.
Make it clear that class disturbance of any kind is unacceptable. This includes: coming in late, sleeping, reading newspapers, listening to music, text-messaging, talking, doing other homework, eating, etc. These activities disturb others and undermine the decorum of the classroom. Deal with these disruptions first through non-verbal cues, catching their eye, to let them know you recognize that they are not engaged in the class. If this doesn't work, you may want to direct a question their way or speak to them after class. Do not ignore these students for to do so only encourages others to join in this kind of behavior.
Take swift and firm action early on, before your authority is compromised. Being able to identify problems before they escalate will help you to maintain control of the class. The basic rule is not to embarrass the student in class. Embarrassment does little to help change a student's behavior and may affect the other students as well. Speak to students individually after class and ask them to adjust their behavior.
Communicate that disturbance shows a disregard for classmates. It is important for students to realize that they are disrespecting their peers, who may want to learn, when they cause classroom disruption. Stress the value of cooperation and consideration.
Recognize that one student dominating a discussion may be a distraction. Class discussion is a great engagement tool, but the other students will tune-out if they feel the discussion is just between you and one or two other students. The rest of the class will become disengaged. Speak to this student after class, explaining the value of involving the whole class.
Keep an eye on students who commonly side-track a discussion, not really responding to the topic or question at hand, moving the class away from the intended content. This student may relate long personal stories which do not really have relevance to the topic at hand. These students can also disrupt a class. It is best to have carefully formed questions that require the answer to relate back directly to the readings or topic at hand. Learn to bring these students back on-topic so the rest of the class doesn't tune-out
Students who make offensive remarks (racist, sexist, etc.), intending to offend, should be spoken to immediately. This behavior is unacceptable and if it repeats, should be dealt with through proper channels. See USC Offices for Help with Student Issues.