If you want to start the GD, you can say- Good morning everyone, we have got a very interesting topic to discuss and if no one has any objection then I would like to begin. The topic name is “__”. In the first step, you have to give brief idea and history of the given topic.
If you want to add some points then you can say – Yes, I agree with you but I would like to add some more points in that.
If someone is going out of the discussion then you can interrupt and say- Excuse me friends, I feel that some of our friends have drifted the topic away from what has been given to us so I think we should come to the topic and continue.
If someone is not speaking, you can say -Friends some of our partners are not speaking so, let’s give them a chance to exchange their valuable opinions or thoughts.
While expressing your thought if someone is interrupting you or arguing then peacefully you can say “please let me complete my sentence”.