For a deep dive into Nudge Theory I recommend Nudge: Improving Decisions About Health, Wealth, and Happiness by Richard H. ThalerCass R. Sunstein
If you Google “Nudge Theory” you will get the wiki definition “Nudge theory (or nudge) is a concept in behavioural science, political theory and economics which proposes positive reinforcement and indirect suggestions to try to achieve non-forced compliance to influence the motives, incentives and decision making of groups and individuals.”
The concept of the nudge has countless applications in the workplace. The reason I’ve included it here is to help managers do a better job at onboarding.
For the purposes of this application, let's consider a “nudge” as a small signal or reminder in the environment that prompts you to do something.
One of my favourite uses of a nudge for managers was from Work Rules! In the Pilot project Google sent reminder emails to managers the Sunday night before new hires started work. The reminder email noted a simple checklist that detailed what successful managers should do with their new hires:
- Have a role-and-responsibility discussion.
- Match your Noogler (New google employee) with a peer buddy
- Help your Noogler build a social network.
- Set up onboarding check-ins once a month for your Noogler’s first six months.
- Encourage open dialogue. 
Consider what best practices you would like all of your managers to follow with new hires. Create checklists and give them to your managers to help with new hires. As a rule of thumb, the more formal the person, the more specific the onboarding milestones need to be.
 5 actions from P.295 in Work Rules!: Insights from Inside Google That Will Transform How You Live and Lead By Laszlo Bock