Hello there,
Thanks for connecting with Careers 360.
Tips for cracking Group Discussion or GD are as follows:

• Be confident but avoid being over confident.
• Talk sense.
• Listen carefully and speak only at the appropriate time.
• Be very sure of what you are speaking.
• Use easy-to-understand English.
• Speak loudly and clearly.
• On the day of GD, dress formally.

For some more information visit following link,
http://www.bschool.careers360.com/articles/7-gd-tips-crack-b-schools-admissions

Tips for cracking Personal Interview (PI) are as follows:

• Be ready with 'must know questions' such as ' why should we hire you?' ,' tell me about yourself?' etc
• Speak confidently
• Be honest to yourself and interviewers. 
• Speak Politely. 
• Drive the interview towards your strength. .
• Don't panic.
• Stay positive with body language and approach. 
• Be thorough with what you write in your CV.

For some more information visit following link,
http://www.bschool.careers360.com/articles/pi-tips-8-keys-crack-personal-interview-for-b-school-admission
All the Best

Hello, for any type of Interview you should have to listen carefully first then you answer  So Watch various english videos on YouTube for good listening. Then for both gd and pi you should be able to know what are dos and don'ts. Doing more and more practice you get confidence. Refer the following links for tips

http://www.bschool.careers360.com/articles/7-gd-tips-crack-b-schools-admissions

http://www.bschool.careers360.com/articles/pi-tips-8-keys-crack-personal-interview-for-b-school-admission