In order to crack the GD and PI, you must be aware of what is happening around you. Make a habit of reading newspapers like The Hindu, ET etc. daily. Make yourself acquainted with sports, politics and economics. Apart from reading newspapers, read editorials, blogs, posts, novels. This will help you in both GD and PI.

Group Discussion: GD topics can basically be of the following types:

Social, Political,Economics,Legal,Technical

So reading news paper and magazines will keep you updated. 

Apart from focusing on the topic, you should also keep in mind certain technical points. Never argue or raise your voice in a GD. Listen what the others have to say and then put your point. Maintain eye contact and make subtle hand gestures. If somebody counters your point, don’t get aggressive.