These links provide up-to-date principles of best practice as well as R code for making excellent graphics.
Wilke, C. 2019. Fundamentals of Data Vizualization: A Primer on Making Informative and Compelling Figures
Healy, K. 2018. Data Visualization: A Practical Introduction
https://www.edwardtufte.com/tufte/
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
Graphics Princriples Cheatsheet
https://clauswilke.com/dataviz/color-basics.html
https://clauswilke.com/dataviz/color-pitfalls.html
https://colorbrewer2.org/
https://cran.r-project.org/web/packages/khroma/vignettes/tol.html
https://github.com/EmilHvitfeldt/r-color-palettes