I personally deeply understand a new language only if I write the same code in two languages, one that I already know very well in your case c++ and the other I'm trying to learn, in your case that's rust. If i just learn from the docs and make new things I miss out on a ton of thinking on why things work the way they do in the new language versus the old one. Essentially it's sort of comparative language analysis

I don't have any fancy techniques for you, I pretty much always go here first https://learnxinyminutes.com, get a feel for the language and then try to build something small using the official docs.