Hey!
This is a very normal feeling before a vacation scheme! It can feel a bit overwhelming because you don't really know what to expect, and so it can feel hard to prepare for it! I've highlighted a few things that you could potentially do to prepare below, but don't worry if you don't have any of this information yet - on most of my schemes, I used an hour or so in the evening in the week to prepare for the next day once I had more information!
I would start by brushing up on your knowledge of the firm so that you feel comfortable talking about their key practice areas, clients, and what differentiates them (this last point being key!). If you happen to know what team you will be sitting in, it is worth doing a bit of light research into that area (e.g. typical work, recent deals that the firm has completed, and any key terminology). However, if you don't know the area that you will be in yet, that is completely fine too - just having a general understanding of the firm should be enough, as you won't be expected to understand the technical detail from day one anyway! A helpful tip that I was told is to make sure that you have your introduction down for your first day so you can make a good first impression - on nearly all of my schemes, my supervisors took me around the department and introduced me to everyone, so I repeated this a lot!
It is also helpful to make sure that you are familiar with some of the key terms used in commercial law and any of the firm's core sectors, just so nothing feels completely unfamiliar when you are hear it (things like warranties, indemnities, representations, etc.). Alongside that, I would try to get a clear idea of what assessments are involved in the scheme (if any!) and think about how you might approach them, so that you aren't going in completely blind! I was encouraged to speak to trainees at the firm who might have gone through the recruitment process recently to ask about how they prepared for the assessments - it might be worth reaching out, or asking your trainee buddy!
I would also make sure that you can clearly articulate your motivations as well, as this is bound to come up at some point, even in informal conversations. If you have a final TC interview at the end of the scheme, make sure that you incorporate insights and experiences from the scheme to show your motivations - they'll want to see that you have used the scheme to make an informed decision about why you want to train at this specific firm.
One thing that is also underrated that I was advised to do before my schemes is to have a bit of a system for reflecting as you go - for example, keeping a quick daily journal of what you did, who you spoke to, and any interesting insights. On my schemes, I would take 30 minutes or so when I got back to my accommodation to just write down anything that I learned that day or found interesting. This ended up being really helpful when it came to the final TC interview, as I could go over this the night before and have clear examples to refer to that backed up my points.
If they have shared a schedule of sessions in advance, I also found it really helpful to quickly brainstorm a few questions ahead of time for each session. Whilst you should ask any questions that pop up during the session, I found that it helped take the stress off in the moment and allowed me to make the most of the opportunities.
Finally, it is definitely worth having a few competency examples in the back of your mind (e.g. teamwork, leadership, handling pressure, etc.) as they might ask these kind of questions in an interview. I personally found it helpful to create a mini bank of my experiences so that I could briefly read over them before any interviews, but you don't need to script anything - I would just be prepared to speak about your past experiences and relate them to your motivations towards the firm or to a specific scenario.
Overall, the main thing is to go in prepared but not overwhelmed - you won't be able to prepare for every possible scenario, and they're not expecting you to know everything! They just want to see that you are engaged, thoughtful, and someone that they would enjoy working with.
You'll be absolutely fine, and I'm sure you'll smash it! Just shout if you have any final questions before your scheme - best of luck!!