You need problems to solve, but most importantly, problems that are highly relevant to you and your interests so you won't give up easily if they become unexpectedly difficult.

You'll be forced to learn new approaches, new tools, perhaps even new languages to solve these problems if they're challenging enough, and don't worry, you'll almost always assume something is easy when it turns out to be a lot harder than you could ever imagine.

Get exceedingly good at breaking down difficult problems into smaller steps you can actually achieve. Try and estimate how much time these steps will take so over time you can get better at estimating how much work is involved in something, which can inform which approach to take or which tool to use.

Above all else, when you learn something and want to know more, learn both in terms of deeper fundamentals, but also in a more strategic sense, like how it is applied, and what are the ramifications of this knowledge, how it fits into the bigger picture.

Remember, it's abstractions all the way down, but also all the way up!