I have a nano 24g and I've changed mine so many times, I've lost track. I've had it set up since November '07, and still not happy with it. Looks like you need more rock though.
On one side of your tank, I'd put 3 of your smallest rocks in the form of a triangle (with a point facing the front of the tank) and put a large one on top of them so it makes a cave. Rocks in front will add more depth.
I try to arrange my rocks so the most amount of light hits them, because thats where corals (and coralline) will grow.