The art of knowing what's going on in your classroom at all time
A withit teacher can see when students are not paying attention, which students can’t follow the lesson, when students are becoming restless, etc.
Some of these techniques you might find useful.
When students talk out of turn and are disrupting the flow of the lesson, I look directly at them and start a loud slow count from one up five. This generally works as the students have been programmed by their Thai teachers from an early age that a full count of five is swiftly followed by something highly unpleasant.