Really depends on what you want to do, what tools are available to you, and how theoretically you want to get.
For theory based academic papers, take a look through previous IEEE Vis conferences to see what's currently being presented -> http://ieeevis.org/year/2018/welcome
For books on techniques and thinking of it, Nadieh Bremer (D3 and Data Art extraordinaire) has some good reviews -> https://www.visualcinnamon.com/resources/learning-data-visua...
For what's possible using D3 take a look at https://bl.ocks.org/mbostock
For other avenues / tools, feel free to email me at sebastian@dashingd3js.com and I can fill you in. It's what I do for a living (for the past ~6 years) and I've been visualizing data online since about 2008 so I have tons of links and resources to share. Just let me know what's helpful.
