Are you attending interview or going to conduct interview?
Your preparations will be different in both the cases.
If you are attending the interview as a prospective job seeker, then gen your self on Labour laws and latest developments and important legal cases which have bearing on IR.
Read ID Act, TU Act,Employee compensationAct and related enactments.
Some of the key sections should literally be at finger tips and some of latest case details.
Besides the attitude of one seeking employment in a field relating to IR should be a confident,good empathetic listener.
IR is all about reconciling differing views and one should learn to be a good negotiator with give and take attitude and limits of give and take.
All the best go with preparation and confidence.