Through Practice, Application, Advancing and Contribution.
Just most of the programmers do in other programming languages they use in
their projects, they do not limit themselves by merely understanding the basics.
In school or in a beginner’s tutorial, whenever you learn new a programming language, you see the same things being taught across these write ups (eg. syntax, control flow, loops, arrays, etc.). Why? Because these are the fundamentals.
Practicing
Converting these as your skill will require you a thorough practicing. Perhaps after reading about arrays, you can start studying Object Oriented Programming. You will find a lot of resources regarding that. Along this stage, you will apparently encounter more errors during runtime or compile time that you tend to solve each time it happens by searching its error code or message in StackOverflow or Google Search.
Application of Knowledge
After you feel comfortable practicing the basics and fundamentals, you will now find yourself not only looking and reading outputs on your IDE’s console but instead, you will be more tempted on applying it on a project based outputs.
You start creating a small project with GUI or form controls using frameworks such as AWT, Swing or SWT. Whilst there are several good other options, for me, it’s better if you try it more in-depth rather than jumping on advanced frameworks you might not even have the chance to configure or touch most of the core functionalities that Java SDK offers.
Advancing
Starting with small projects is a good jumpstart on improving your programming skills, but then again, the industry is in need of a more skilled and knowledgeable programmer who knows the hows and whys in a scalable project.
This is where you consider yourself to be more expert on the technical side of what you know. You may need to start reading topics regarding software tests, threading, software architectural patterns, asynchronous functions or maybe dig deeper on how JVM actually run.
From this point, you can now confidently justify what’s happening under the hood whenever you run and compile your code. It’s also makes reading someone else’s easier for you (well, depending really on how it is written or maintained).
Contribute
Last thing you need to consider doing is to contribute. Either start with GitHub’s open source projects, read someone else project’s documentation and code base, find a bug and submit a patch or start becoming a tech evangelistwhere you can do tutorials, write blogs or even teach in workshops especially for the young and aspiring programmers.