I envision two ways to aquascape a corner tank. One is to have the rocks predominantly centered. The other is to have the rocks on both sides forming a channel in the middle. In this arrangement, the deeper middle will give the tank greater depth perception. Personally, I prefer the latter. I've never had the chance to do something like that but have always wanted to.
As with any aquascaping, keep it "open" and "dynamic." Lots of tunnels, caves, ledges, and pillars creates a very natural and interesting look.