An interesting exercise in worldbuilding is trying to figure out how the different classes fit into your world. This serves a couple purposes; it gives you a framework to explore and expand your world and it gives you some direction for your players. If a new player is curious about, say, invokers you could tell him about the Bretani Academy where priests of varied faiths train in secret for the day when the primordials will try to retake the world.
So the next time you’re just sitting around or bored, try this. Pick a class. Now come up with three different backgrounds for or examples of that class. You don’t need to restrict yourself to the exotic classes either; as generic as a fighter is, it can serve as a great jumping off point for defining a mercenary troupe, a military, or a nomadic desert tribe known for wielding their signature khopeshes.