Hello Bindusriram,
I had the opportunity to attend a lot of sessions on Group Discussion in my school and college life. From whatever I have learnt, I can suggest that there should be a systematic approach to G.D. First of all there should not be more than 8-10 students in a group. Out of these, you can select one of the team members to be the group leader. Give a simple topic and ask them to communicate in English only. At first it will be a little difficult but gradually, they will gain confidence. Ask each member of the group to say some points in favour or against the topic. Then, the group leader will write down all the points and recite the conclusion to all the other groups. You can keep changing the group leader in some duration. But, the main aspect of G.D. should be that we need to DISCUSS and not ARGUE.
For Interviews, conduct mock interviews and encourage them to speak. I think unless and until they get the confidence to speak, it will not help. Ask them to tell about themselves, their hobbies, etc.
I hope this helps.
Thanks,
Pratik Raj