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

Green, S. DataVizChecklist

Graphics Princriples Cheatsheet