After you've finished R4DS, it may be useful to find some data to just play around with and start asking your own data science questions! When new R users have had some good initial instruction, I normally tell them to just have a go at their next project using R rather than Excel or their usual tools.
If you're not in the position to do that (if you're not in a data profession, or your work is weird about using different tools, or you just can't commit to R in a professional space right now), consider the #tidytuesday data project:
Every week there's a new data set to have a go at analysing, and a supportive twitter community based around sharing analysis, visualisations and code. I personally learned a lot from playing around with these fun data sets and reading other R users' #tidytuesday GitHub repos.
Some good ones to have a look at to see the cool stuff people have done in R are: