So, I like whiteboard art. I use it in the classroom and post it on my blog. I've been working on my craft for several years now, and thought it might be time to record a few thoughts.
Whiteboard art is a limited medium. Expo markers, my preferred tools of the trade, only come in about twelve colors (at least that I can find.) They don't admit of blending in the way that chalk or pastels do. The fact that adding a new line to an existing line with an Expo marker can erase it also provides some unique challenges to drawing and shading. Filling in solid objects is a real bear.
Given these constraints, whiteboard art lends itself to cartoons, pointillism, and impressionism. Getting into the right mindset for the latter two techniques can be a little rough at first, and I recommend stepping back from your work frequently in order to get a sense of the overall effect. Spending some time with a volume of impressionist paintings also helps. As far as cartooning goes, I recommend getting into a web-comic or two. They're free online, so there's no problem with accessibility or cost. They also tend to be a little more realistic than what you find in the Sunday papers while rarely sporting the frustrating complexity of many modern comic books.
As a final note, the guys over at Wheatstone's The Examined Life are my real heroes when it comes to technique. The videos they put together using time-lapse and whiteboard art are amazing. Nothing gets the creative drive going like a little inspiration, so if you're going to attempt any whiteboard art, I recommend checking out what these guys are doing to get the creative juices flowing.
That's all I've got right now. If anyone has anything to add, don't hesitate to jump in.