[exDM69]

Quite simple: write more code. Go outside your comfort zone and do a project that is unlike anything you've done before. Write an interpreter or a compiler or an operating system skeleton or something else you've never done before.

And if you don't come up with an interesting learning project, you can always learn new programming languages. I've found that the best learning experiences have been the languages that least resemble what I use daily. I'm a C programmer but for learning purposes I recommend learning a Lisp, ML or Haskell and Prolog. An alternative to Prolog is going through the logic programming chapter of SICP and writing your own Lisp-based logic programming language and having fun with that (I actually used Haskell + Parsec to implement a logic language).