My process for learning a new language has been to focus on the fundamentals. Think about how you would teach Python to a total newbie and do that with JavaScript. You already know how to create a working program and are probably comfortable with a number of patterns. Your brain will figure out the high-level stuff on its own so don't worry about writing fancy structures or algorithms. You need to know the basic building blocks of the language.
The only specific advice I would give is to separate learning ES6 features into its own lesson. Start by using good old JS inheritance, creating instances, constructors and all of the pillars of the language. Learn classes by rewriting the same code with new syntax, because JS classes really are just new syntax for the same old patterns.
Before long you will come up with an idea and want to build it. If you focus on being productive too soon you will only look like you know what you're doing... until you don't.