Create lines. In this case lines are made by a stone wall, and Anubias attached to corkbark on the back glass at varying height.
 
 
 

The rocks were siliconed together in an arching wall before being put in the tank. Gravel and Java moss fill in the cracks.

Empty rows between plants that are allowed to grow over, offer interesting views deep into the lush background.
 

Arranging clumps of grass close to wood has a natural look, and the dark wood is a nice contrast behind the plants. Even very small, rooty wood is great in this scenario.