I figured I'd start off slow by following a decent set of tutorials on the Arduino. Independent of experience, it's always been helpful to me to get a decent idea of "platform workflow", or how engineers and designers approach development on a platform by walking through a few examples. For instance, I've noticed that PIC, BASIC Stamp, Motorolla, and ARM hackers tend to approach the design process differently: Stamp guys tend to prototype on the fly, and write code while they run, PIC guys tend to draw schematics before building, and Motorolla /ARM (and other low-complexity sub-PowerPC/x86) tend to go through more elaborate pre-design, pseudo code, meta/block diagram, and schematic drawing before finally building and coding.
For purposes of the Arduino, I've chosen to start here:
LadyAda Arduino Tutorials
I found the link on the Arduino main tutorial page