Just a simple thing as learning it all: http://processing.org/learning/
The wonderful books http://processing.org/learning/books/
The inspirational work of others http://processing.org/exhibition/, http://www.openprocessing.org/, http://www.vimeo.com/tag:processing.org, http://www.youtube.com/group/processing
The endless discussions in this excellent community where even boring problems becomes fascinating http://processing.org/discourse/yabb2/YaBB.pl
Experimental solutions come into light http://processing.org/hacks/
Processing has inspired me more than any other platform so far, apart from typography in general. Processing stands for creativity in the rawest of formats. Amazing, inspirational, mindbending, attention altering and simply wonderful.