Every new hire is assigned a "coach" on their team, another engineer. We have a formalized onboarding plan with first day, first week, first month expectations

Every new hire is assigned a "coach" on their team, another engineer. We have a formalized onboarding plan with first day, first week, first month expectations outlined for both (set up such and such software, get these repos running, teach/learn about the product/architecture/tooling, do a deploy + rollback, etc etc). The coach picks up the easier tasks and pairs with the new person. It's important that these are not throwaway tasks but actually contribute to current team goals - that way the new hire is properly part of their new team and absorbs relevant team conversations through osmosis. This works fantastically. It's a bit overwhelming at first, but results in a functioning, contributing team member in a very short period of time. New hires are expected to push code to production within first week (often happens within first couple of days). There obviously needs to be a lot of cultural support for this. It certainly helps that we have a solid culture of pairing, so all of this is quite natural. You'd have to modify this a bit if you're the only coach to three new hires. At a high level though, the approach is - have a plan, have a helper, pair on relevant tasks, rinse and repeat until both are comfortable.