I'd wait til you've joined then go on the org chart and offer to take people for a coffee chat once you've figured who you want to speak to. Sounds very Love Island but that's generally the most effective route.If you’re a future trainee at a firm and know you want to qualify into a certain team, would it be helpful to begin reaching out to associates in that team to build relationships before you join the firm or would that be too early and/or not affect your chances of getting that seat at all?
Reaching out on LinkedIn etc might be a bit keen. Just my 2 cents.