Books are good if you do the exercises alongside each chapter. Blog posts are also useful if you need a breakdown of a specific technical subject. However the best way to improve, in my opinion, is to play in your mind with mental models of whatever you're studying. Thus, if you wanted to be a great programmer, I think you should build up mental models of many reputable open source software projects and play with those mental models. That basically builds up your neurons to quickly recognize patterns in new software situations.

It's like music. Play a lot, listen a lot, and you'll build up a mental library of riffs and sounds that you can use to build a song or phrase. If you play with software a lot then you'll see those patterns and become a better composer, and you'll also be comfortable answering questions about optimization, architecture etc.

But not huge on blog posts. Not engaging enough.