We pair new hires, regardless of ability, with a mentor. They have access to a full checklist of on-boarding tasks and an actively maintained Basecamp.
Perhaps the key point is that we do not have "hidden" discussions. Even the voice discussions have notes taken and recorded, and planning sessions are done via a recorded Miro board. Day-to-day project management is entirely in Basecamp and Slack. Anything in Slack that's worth noting is made into a Basecamp task for posterity.
We're a flat hierarchy, and we encourage team members to be vocal about what they want to work on. The entire team plans quarterly targets and goals.
It's, honestly, kinda awesome.
Edit: we're less than 50 people, and that makes it easier not to have a hierarchy since most features are built by one or two people.