My large 3ft tan is set up sort of like a river bed. I used propagating sand for substrate; It's like sand but with small bits of gravel in it. Then I randomly placed a few natural colored stones along the sand. Which gave a nice natural look.
I used large rocks to create caves, and a piece of driftwood forms an arch across the middle of the tank. I planted banana lillies on the driftwood, and a long reedy plant called vallisneria in the substrate. The plants survive in low light so the axies dont have to hide for the light for too long during the day.
I'll try and get some pics, but my camera is playing up at the moment.