pls help regarding visa interview in india for us

hi,

one of my friend is going to face interview in india as her husband has got the us citizenship n now wants his family i.e. my friend n their child to be with him. he had applied for their visa n greencard which has been approved n now they will be going to face the interview.
Can someone help with the kind of questions asked in the interview n hw to prepare for it..pls guide

thanks in advance