The last update of this post: 2019-01-23.
Below is a checklist that I wrote for my own purposes. I helps me to be sure that I did what I should have done before release a new version of R package to CRAN. Maybe it will also help others.
See what new Hadley recommends:
Update R & packages:
RStudio (stable or preview version).
Update your package:
Check unit tests.