For developing skills, a simple answer is learn a new language. Do a personal project in something dynamic and object oriented (e.g. not C). C is a great langua

For developing skills, a simple answer is learn a new language. Do a personal project in something dynamic and object oriented (e.g. not C). C is a great language and you will be happy you know it. But learning new languages forces you to think differently which allows you to think differently in the languages you already know. Also knowing how to build web connected GUI apps in an afternoon is also a very liberating skill for a developer (Python, Ruby, Clojure are all good choices; or C#, Java if you wanna stick somewhat closer to what you know).