Code reviews can be difficult, how do you teach the hard bits?

Code reviews can be difficult. Do you know of good ways to teach the hard bits. Reviews of code/design/requirements are good, but some aspects are hard. Are you aware of resources that teach the hard bit of doing code reviews?

This is talks about the problem of pair programming, it is a less than perfect solution. It has some advice on pair programming:

https://sking7.github.io/articles/810360223.html

Anyone seen any good advice on doing reviews. Some issues:

• Balancing reviews as a teaching tool or a QA process.
• How to improve ROI of the review process.
• Checklists
• Number of devs reviewing a document.
• Teaching non-programmers to review requirements docs.