I've been wanting to learn Hammer and get familiar with the source engine for some time now, what would you guys recommend I focus on? Aside from the obvious of learning how the editor works. My goal at the moment is to make basic maps with it and eventually throw my own content in it. I'm comfortable with the UDK and CE2 but as an aspiring environment artist, I've never focused on making maps in them, just getting my art in engine and setting up materials, lighting, etc.
Hopefully the question isn't too vague. Perhaps a better way to rephrase it, knowing what you know now, what do you all wish you learned when you first started?