Check out the book "Work Rules!" by Laszlo Block. It describes the onboarding process at Google and specifically what impact certain behaviors had on retention

Check out the book "Work Rules!" by Laszlo Block. It describes the onboarding process at Google and specifically what impact certain behaviors had on retention. It's a useful read and the practices they've adopted can be utilized in any size company as they're fairly straightforward. Things like: use a checklist, assign a mentor peer, etc.