This is the most useful: group activity, don't become the leader as they x you off instantly, don't say to little but just say enough to keep the activity flowing in a equal manner so everyone contributes.
1:1 interview is easy, have some questions with the interviewer to keep it going back and fourth, also do some research about ur role to sound like you know what your going to be working with and who your working for, ie deloitte.
Presentation during 1:1, I'm not entirely sure what the Presentation will be about but im about 70% sure it'll be about how you can improve the tax system, find some flaws or current tax procedures that can be improved and memorise it.