In addition to simply expanding it, we also rotate the layout. Sometimes we do so because we found one plant impeded our access to another, or a certain plant didn't fare well in a certain spot. Sometimes we rotate to run away from dormant bugs, like the Colorado potato beetles that absolutely ruined last year's potato crop. But mostly we rotate because of soil nutrients and sheer love of variety.
Here is last year's garden layout:
And This coming year's layout (please note that fence posts are decorative and not for measurement purposes):
And, in case you were wondering why I bothered to color my own version of it here is Nick's idea of a blog-worthy garden diagram: