Consider completing "Advanced R, Abridged" and "Git 101 Exercises" first.
"Advanced R" by Hadley Wickham is widely considered the best resource to improve your knowledge at building an R package. This guide is designed to give you the most essential parts of R Packages so that you can get going right away. It still will take a long time, but not as long.
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- Read the following chapters of "R Packages" by Hadley Wickham: