Beyond the basics, it's also quite useful to pick out a piece of art or an effect you like and attempt to recreate it. You'll learn a lot of tricks very quickly that way.
Processing, p5.js, Max/MSP (if you want to do audio/video), CFDG (context-free design grammars). CFDG (contextfreeart.org) has a lot of bang for the buck in terms of effort in to quality of output out.
Beyond the basics, it's also quite useful to pick out a piece of art or an effect you like and attempt to recreate it. You'll learn a lot of tricks very quickly that way.