Thank you so much for your answer. I've also read that successful TC offer holders often go out of their way to knock on people's doors/ go up to people to speak to them (not during lunch but during working hours) to make themselves known. Is this actually typical and recommended? Or should I just get on with work and focus on socialising during lunch/break or events?
In my experience it can also be the case that some hyper-social vacation schemers end up not converting for this very reason. Firstly, like Jessica pointed out, doing this will likely mean you have less time to invest in your work; and for many firms both the quality and quantity of your work product is a key assessment criterion. Secondly, being extremely socially proactive during work hours might not be as best received as you would think by the people you are interacting with. While they might not say no to meeting with you out of politeness, many of them also have very busy schedules and are constantly stressed by deadlines. As such, prologued meetings with no obvious purposes outside break times might actually annoy them. This is why
I would advise you to first speak to your supervisor/trainee buddy before you decide who you want to invite for a coffee chat. They might be able to tell you a lot more about which people or which teams are more and less busy at the moment; and which specific team members enjoy chatting and socializing more.
They might also be able to tell you whether it is better to approach certain people in person or via email/internal messaging systems. At any rate, in my experience socializing beyond the point of your team members generally knowing who you are and seeing you as a nice person does not impact your conversion chances that much.
That said, I will caveat this by saying that it may not apply at specific firms. Different firms have different recruitment strategies and assess vacation schemers on different criteria. Many will care a lot about the work you do, but I know some that place only minimal importance on that.
My best advice is to try to speak to graduate recruitment and current/future trainees and get their view on the following questions: what are the most important things the firm is looking for? How would you advise a vacation schemer to invest their time? How should I approach people to get to know them? You should then modify your strategy accordingly.