Law

GD: Generally the trend is to have discussions on current topics, which may be legal, finance related, or social issues. In other words, you may prepare by reading newspapers and competitive magazine to study the trend of topics in news. Again, GD/Essay/GK, there is no defined area of preparation, but general awareness helps.
My experience: This is in May 2009 when I had my GD. We were a group of 7 and an old man as our moderator. The topic of discussion was "Sub-Prime Crisis in USA and how has it affected India" (If you remember this was a hot topic in 2008 onwards for a long time). Anyway, the discussion lasted for 35-40 minds. We were not instructed to draw group conclusion and put our own views in couple of lines to end the discussion.
Tips:
1) Listen to the topic carefully. If in doubt, ask for clarification 10 times until you are clear.
2) Carry a Pen and a paper.
3) Be polite and always address to the group.
Interview:
Conducted on the same day after your GDs are done. I had a panel of 2 (Dean, SLS Pune and a Asst. Professor). The questions were quite general in nature such as:
1) Where are you from?
2) Why do you want to become a lawyer (since had no humanities background)?
3) Some legal questions relating to criminal law:
Is captial punishment good or bad?
4) What is your backup in case you don't get through to the law school?
In nutshell, they are trying to know you and your views in general. Be calm, patient and have confidence to make it through.
Hope this helps.
All the best.