Practice, practice, practice. I always suggest that you should start by writing your unit tests on the language you wish to learn, but this is valid only with languages that play together. For instance, to learn groovy i wrote my unit tests for my JAVA code in groovy, now i'm repeating the process with Kotlin... Other than that, do as many KATAs as you can find online. "codewars.com" is nice, too. But keep in mind that "language(s)" are just tools, you reaaly should focus on a better grasp of CS concepts and fundamentals, the tools will be obsolete before you notice.