When I was near landing my first job in the web development industry, I met with the agency's senior-most developer. He was kicking me off on a freelance project that the agency was going to use to assess my viability as an employee.
To be able to succeed on that project, I had to learn Ruby on Rails, which is no easy feat for a person almost brand new to web development. Knowing I was very likely in over my head, I asked that lead developer if he had any advice for me as I was getting started with Rails, thinking he would point me to some useful books or tutorials. But he said something entirely different:
"Put all the code you write on GitHub."
It didn't really mean much to me at the time, but I still took the advice. Looking back years later, I feel like that was one of the most important ideas I've taken with me throughout my career.
So now I pass it on to you, as I do with junior and mid-level devs on my team. But I'll add to it by saying that the code on GitHub should also be publicly available, and that you should share it after you publish it.
I find this idea — publishing and sharing even your shittiest code and dumbest ideas — to be important for three reasons:
You aren't the next Zuckerberg. (Do you really want to be?) For every developer that makes a million dollars from writing code, there are a thousand (or more) that don't. And there is plenty of time to go after the gold. But as you're starting out, focus on getting better at writing code. The million dollars can come later.
That said, if you feel like you need the money, then ask for more money for your main job. If you are doing good work, you can get paid for it during the day. I know it's not as cut and dry as that. My point is that what you do on the side should be for fun, at least initially.
Building a community around the work you do is going to be more beneficial for your career than a little bit of money. If you can build a product that other developers want to use or contribute to, that's going to get you noticed.
Once you have that community you can attack that big, million-dollar idea.
Last, you're very likely using open-source software to build the things you are building. You have a responsibility to give back to that software that has served you. You're now part of a community. You can give back in money, sure. But you can also give back in code. Share what you've done with the tools that others have graciously built for you for free.
Yeah, you'll make some mistakes along the way. You may publish a private key. Your GitHub account may be littered with awful code. That's fine. You can recover from shared keys. You can clean up your account later. Or not. It doesn't really matter.
What matters is that you're passionate about the projects you're working on, and that it's fun to work on them.
So go make something. And then share it!