Why behaviour matters
Behaviour is like breathing, is it's not going smoothly you should be paying serious attention to it. Now imagine spinning plates on stage and the breathing starts to get irregular. Keeping the majority of the plates spinning is important and not resolving the breathing can be catastrophic. Here is some simple rules to make a learning environment more effective.
Set ground rules of how the learners want their learning to be fair
As a teacher include your ground rules too, including be kind, be honest, and get great results. With the caveat of Be kind, but not so kind that you are dishonest. Be honest but not so honest that you are unkind. Only by being kind and honest are we to get great results.
Acknowledge the poor behaviour and keep moving forward
A good rule to this is to have short eye contact with the intention of acknowledgement that the behaviour is not as expected. Moving closer in proximity whilst talking, and facing the way they are facing can quash light behaviour issues without distracting other students.
Redirect the class and give private feedback
If non-verbal feedback is not working, redirect the learners to talk in in pairs about the objective of the lesson and what is means. Give calm, quiet feedback to the learner not behaving. Give yourself TIME to work with the learner, you have more time than you think.
Brief stop and start of learning
Stop the learning (briefly) for everyone using the ground rules and publicly address the behaviour in what the educator expects. Clarify with an 'I' statement of what you expect and leave an 'out' for the poor behaving learner. The 'out' naturally allows for an excuse (first offence) but address it without punishment. If the student is going to disrupt again then address it more severely but keep the tone light.
The screeching halt
The learner has done something egregious it is acceptable to stop the class, make the environment safe, isolate the learner to a separate location (in the classroom or outside of it). Address the issue with the learner (when isolated) about what's going to happen next. Leave them isolated from the class to reflect about how they are going to improve. Address the class to ensure safety of all pupils is the most important priority of the school. Give yourself time to think about what they did, and how it impacts the students learning. Match it with the punishment.