Programming

Just keep coding. Feel free to use as many guardrails and tools as necessary in your IDE (linters, auto completes, mouse over definitions, etc) to make it easier. To use a language metaphor, you want to be focusing on how to communicate, not on things like who vs whom, the subjunctive case, or adjective order. If you need projects, there are plenty of lists out there, but doing something you actually care about and breaking it down into chunks small enough to do is probably more sustainable than a bunch of random tasks someone else recommends.

As for learning new languages: when you have to. If there's something specific you want to do and it's only done in a specific language, then go for it, but there's nothing inherently good about knowing multiple languages, especially if spreading yourself thin prevents you from improving in your main language (or is detrimental because it muddles the patterns you've learned in each).