Ask HN: What is the best way to promote your abilities as a developer?

I am a web developer and I have been working in this area for 4 years. But I have not really built something that could really show my abilities. And I have been wondering if I should be a good stackoverflow member, write articles, work in open sources projects, put my side projects online ? I am not looking for a job right now, but I want to have something valuable that could help me find a great one if I need to.