Hello Roydilson,

The most important quality needed to clear GD is KNOWLEDGE.

Knowledge on all sorts of topic right from politics to history to geography to travel to cuisines to meditation to sports to any topic you could think of on earth. 

This is possible on through Reading. So Read anything and everything you can lay your hands on. It can be encyclopedia or magazines or a google search etc.

But just reading and storing knowledge is not important. Being able to Communicate it is also very very important. Without being argumentative, supporting your ideas with facts and logic and trying not to be very convincing but being confident of your knowledge in itself will convince others is the main crux of communication.

Stick to one point only. Listening to others and changing your views would have a negative impact on others. Sometimes, others may have a valid reason, but you must be polite and be bale to defend your point.

Being a leader but not bossy is another trait on winning a group discussion. If you are confident, you can start the discussion, how you pitch in the middle of someone else talk is also important and most important is helping others in the group, the quiet ones to speak is an art.

Maintaining a calm, confident and an approachable demur is important. Maintaining eye contact is also essential. Thus wearing something you are comfortable is a must. Just to get accustomed to the environment,  see is you could be friendly with the others who are in the campus, few of them would be in your team. At the sametime, greet everyone you meet helps you relax and study people.

Hope this helps.

Wish you good luck...