OP mentioned reading Gang of Four, which could be considered fundamental knowledge. More generally, by fundamentals I mean a pack of things including CS101, ba

OP mentioned reading Gang of Four, which could be considered fundamental knowledge. More generally, by fundamentals I mean a pack of things including CS101, basic understanding of C (K&R), data structures and algorithms (those available in coursera courses are enough to get the basics), good use of source control systems, and project architecture basics.