When I first set up the tank, It was like a small bridge, and I only had about 25 lbs, out of 3 rocks. I chopped one up so now I had to redo it and I had a TON of room to fill. I filled in behind the 2 existing rocks and stacked up the back for a slope type deal. Then on the left side I tried to wrap it out into the sand a little more for some lower light and delicate corals (when it comes to warfare). Most importantly to me, I make sure that SPS are separated from the others so they can be catered to, and the rest on the mid/bottom so they dont get pounded by the flow.
If I had a larger tank, I would make 2 islands on opposite sides. One being a really tall, spire-ish one and the other being more of a mound, with it leaning on a tank wall. It looks really cool in my head.