I want to reiterate this point, for a while I would make it a point to check the latest questions on Stack Overflow for various languages I was decent at and try to answer a couple every day. There were lots of questions in which I knew 80% of the answer, and the process of discovering the last 20% always helped me learn something new. Between just reading answers to random questions and doing that, I found it to be a really awesome way to become a more knowledgable developer.