R Book: R for Data Science by Hadley Wickham, Mine Çetinkaya-Rundel, and Garrett Grolemund.
Data Visualization Book: Hands-on Data Visualization
Book on Computational Social Science: Bit by Bit
Course: Harvard on Edx - Data Science: R Basics
8-week R course with great best-practices tips by Stephanie Hicks
Hands-on-practice: Datacamp
For more free R books, see Dr. Mine Dogucu's website
Twitter: Apply for Twitter's Academic API
A Guide for a CSS Career: A Three-Step Guide to Training Computational Social Science Ph.D. Students for Academic and Non-Academic Careers
Learning: Live R course for beginners