These links provide up-to-date principles of best practice as well as R code for making excellent graphics.
Healy, K. 2018. Data Visualization: A Practical Introduction
Stephen Few’s books and blog
Kabacof, R. 2018. Data Visualisation with R
Peng, R.D. 2020. (Exploratory Data Analysis with R](https://bookdown.org/rdpeng/exdata/)
Green, S. DataVizChecklist