Dpending on the fish, I either have my tanks bare with only gravel or I fill the tank with driftwood and plants....I stay away from rocks as much as I can because they can cause scratches on the fish.....
My 55g went through a ton of decoration changes until I decided on Malawi cichlids. I'm super happy with the simple rock stack & sand combo. I have 65lbs of lace rock, 55lbs of Caribsea Moon White sand + the fish. I laid eggcrate on the bottom just in case too.
I've found it's so much easier to maintain and keep clean. I also love how it looks now, here's a pic:
Use floating plants or plants that are attached to driftwoods. Java moss, Java ferns and anubias are a few that can attach themselves to any decorations. They are also pretty tough.