Identify problems and fix them.
Automating something boring, elaborate or repetitive is an easy way to get started.
Anything that can save people time or repetitions or just less human intervention in general or for greater speed or accuracy in something crucial is a valuable skill.
Also, another way to showcase how you can generate value is by coming up with something creative or by being able to show you can solve hard problems with elegant design.
Then just get a github account and put some code. If you build hardware things, find any mean of publishing appropriate.
You can even have a free blog or website on github (you can even monetize it according to the license user agreement) for any of your project and you personal account for you portfolio.
Then make your CV in function of what you have in terms of competence and elaborate on each point of the cluster of related abilities.
Write the things from your previous involvement in a job or open source projects you have or contribute to in a way that relates to potential job offerings by describing what skills you needed to accomplish the tasks you previously had to accomplish.
Don't settle too low in terms of salary, do not ever accept unpaid internships or accept any kind of weird payment arrangements unless you live in the third world, ever. If you undervalue yourself people will undervalue you.
Try to show that you're passionate about what you do and be cool with the people you meet, be honest about what you know and when you don't stay relax. Never take anything personal and always allow your failures to become an opportunity to learn.
If you ever face hard interview questions, try to ask about as many of the constraints related to the problem can have an effect on your solution. Break down problems, sometimes there are parts that you can already solve and work on the chunks one by one until they're all separately proven then stitch them together somehow.