Onboarding the first 30 days
The first 30 days determine whether you'll keep this person 30 months. Most shops wing it.
Decide what 'fully ramped' means before day one
Write down what the person should be doing independently by day 30, 60, and 90. Without this, 'they're not getting it' is a feeling. With it, it's a checklist you can both look at.
Schedule the first two weeks hour by hour
Showing up day one with no plan teaches the new hire that this is a chaotic shop. A shared calendar, who they're shadowing, what they're learning, when they're getting feedback, does more for retention than any orientation packet.
Feedback in week one, not month three
A 15-minute end-of-week-one conversation, what's working, what's confusing, what's surprising, catches problems while they're still cheap to fix.
Don't leave them with the worst trainer
The most senior person isn't always the best trainer. Pick the team member who explains things patiently and accurately, and pay them a small bump for the time.
Take your version of this question further
This is one operator-tested angle on the question. Your shop, your size, your trade, and your team change the answer. Ask your specific version inside Ask a Shop Owner to get a response grounded in how owners like you actually handled it.