For those people with Law interviews, there isn't really that much you can do by way of preparation to be honest. You will be given a case judgement to read a few hours before the interview and then you will be asked questions on that for 80% of the interview.
The other stuff is general things about A level subjects, and extra curricular stuff which is mainly just to make you feel more comfortable.
I remember being asked to define some things- 'national security' was one i think.