Answer:
Listen
One thing to keep in mind while participating in any formal or informal discussion is to listen carefully. One must understand the point of organizing a group discussion. We want to listen to people's perspectives, assess them on the basis of their skills etc. Listening is one such important skill.
When you try to listen to the other person's point carefully you'll be able to -
Refine your own points.
Counter their point if necessary.
Notice their mistakes and avoid them etc
Listening here does not mean you will not put forward your points. No. Be an active participant but keep your ears open.