programming fundamentals (data types, algorithms, control structures, logic, etc.) .
the diffe…rences between browsers (the event model, for instance is different between Internet Explorer and other browsers) .
functional/procedural/object-oriented programming .
experience: create your own projects, work on open source projects, this will give you experience and allow you to learn from more experienced programmers .
tenacity: it doesn't happen overnight; as with anything, you will have to work hard to become an expert (MORE)