Here's some thoughts/ideas at random in point form:
-It helps to slope the gravel downwards from back to front overall, even if you're adding terracing and such.
-I find straight peices of wood uninteresting personally. Curves, branches, knotts and so on will help.
-Rock is a nice addition; find ones with interesting faces or textures. Be sure that they're aquarium safe.
-You'll want to familiarize your self with some basics about color composition and the golden mean.
- Draw your tank before you put it together, even if you're bad at drawing. It helps to visualize.
- If you have any fine ground cover going in, consider a dry start.