I recently finished up my undergraduate education and realized there were certain large important parts of computer science I knew very little to nothing about (I stopped really taking CS classes to go take a lot of advanced math courses my last two years, which I'm not certain was the best decision, but it wasn't a bad one either), so I've been thinking a lot in the past few months about what my best options were for learning about subjects I'm weak in or knew next to nothing about. (E.x.: implementation of databases, OS design, AI, HCI, and other fields) Putting that into words wasn't too difficult, and hopefully it'll make figuring things out easier for someone else... I tried the reading papers and textbook approach, which is part of why I wouldn't recommend them.