Hi,
I've done the AC a few months back so the AC may have changed since then, but here is a short summary of my day:
1) Partner interview: we received a case study in the morning and had some time to look over it and prepare for the interview. Case study was business related, you had to present the most important commercial issues in the scenario and practice areas you'd involve in the deal from the firm. Generally the case study was much better than what I expected, and the partner I had my interview with was suuuuper nice. After discussing the case study I had a competency based interview with the partner.
2) Group work: we were working in a group on a presentation for two associates who were in the room and observing. I'd say make sure you're listening to people and generally being cooperative, cause we did have a guy in our group who clearly was not listening to everyone else and just pushing his ideas, and that was definitely noticed as not very good. The topic was interesting, and we actually received materials to work from, so it did not require any prerequisite knowledge for sure, just analysis, structuring and presenting well.
3) Speed networking: we had 6 mins per person, and 6 people to speak to. They were mainly trainees from what I remember. We were told when to change people so that was easy. The people I was talking to had set questions I had to answer, some of which were 'fun' and others business related (but not testing you on current events - just generally business related) - This was the part of the day that I was most nervous about but turned out to be the most fun as I got to speak with current trainees and ask them about their experience.
This was my order on the day but the order varied for applicants as we were split in two groups.
In general i'd say the most important thing was to be excited about the firm and to know about its strengths, recent deals, etc. Definitely smile a lot and be attentive. I really enjoyed the day (as weird as that sounds) and found everyone very friendly and approachable so do not stress too much (I know, easier said than done).
Good luck!