My package, poppr, has been on CRAN for over six years now and it has received more than 400 citations and just north of 70,000 downloads from the RStudio cran mirror. I can think of three reasons why this package has been successful:
Our lab gave several workshops using our package over the years We have written extensive documentation with both web site and package documentation. I actively maintain and answer the vast majority of questions that appear on the poppr google group.