Know that sometimes, actions are louder than words.
Walk back to stand near a talking student.
Try silence.
Try not speaking yourself until everyone is demonstrating desired behavior.

Try establishing strong eye contact.
Rather than put marks on the board for poor behavior, it is better to put up a number of marks or flags or stars, etc., for every student. Do not call on students to read or answer questions in predictable routine.
Be quick to change to a question-and-answer method.
Lead students to deduce life principles from your academic content. Structure the listening task for your students.
With younger students, a special puppet.
Recognize small increments of improvements in behavior and encourage them.
Try focusing on a student who is demonstrating good behavior and compliment it.
Try asking the student with offending behavior if you can help him. Try lowering your voice.
Recognize that persistent misbehavior is often a sign of deeper need, usually for attention or love.
Be patient.