It's a performance just like any other, so just like any other self-taught performer learns their art-- some combination of training, research, practice, and seeking critique. I've known a handful of people that found their local Toastmasters International clubs to be a great start. I've known about as many people who dramatically improved their off-the-cuff social fluidity by taking improv comedy classes-- which is pretty admirable but I think I'd rather repeatedly whack myself in the kneecap with a ball peen hammer than take an improv comedy class. (though maybe that means I should take one? I dunno.)
You can go a long way with LMMS or Ardour and free sample packs. Most big sample production companies provide royalty-free samplers. The free stuff from Sonniss (GDC freebies) and Black Octopus Sound could last an entire career. Throw in the free Komplete Start (or Helm and Surge if you prefer open source) and you have all your synthesis needs covered: https://www.native-instruments.com/en/products/komplete/bund...
If you mean acquiring facts, maybe not. If you mean getting better at a skill such as programming or playing the piano, how could you possibly get better without challenging yourself?
It's rational for most candidates to study interview prep books because that is what the majority of companies want. Not saying I like it, but why would you want to filter out candidates who are just using basic common sense?
