Hey Alice!
I also did the FF AC a couple of years ago and made it to their Vac Scheme as a result.
The structure is as
@Noodles52 said. I would say in general they are looking for people to show a business/commercial awareness on the day. Many of the candidates had not done the GDL/LPC in my cohort, and still made it to the VS. So, try and approach the group exercise/written exercise from that perspective.
The written exercise was quite palatable for my AC as well, a tip would be to make sure you are keeping track of time and not writing a novel. The firm is looking for people to be as concise as possible with this task.
For the group exercise, I would recommend to not speak over people while trying to encourage the quieter members of the group to contribute. FF is big on collaboration and teamwork, so try to focus on fostering a collegial approach.
The partner interview is always my favourite part of these ACs, and here, definitely don't be afraid to be yourself and have a sense of humour. They want to get to know you as a person to see if you would be a good fit for the firm, and not a retelling of your CV. There were lots of competency based questions, and you can find loads of them online to practice beforehand. I found making a list of the possible skills I could mention with matching examples useful for this.
Finally, for the presentation, do NOT go over time.
DM me if you have any more questions, happy to help!