> Learn data structures and algorithms. Understand finite state machines and context free grammars. Learn at least some mathematics. Discrete math, Boolean logic, and statistics. Learn how operating systems work, networking, databases, compilers, machine code, low-level details like registers and the cache hierarchy. Learn more obscure programming languages: like Lisp, Prolog, Haskell, and Forth.

Also, these may seem like separate subjects but there is some overlap especially once you work with things like databases in production at some scale.