i've found that plain black sand/gravel and a plain black background really brings out the colours of your plants and fish, a big shoal of cardinal tetras weaving in and out of some lush green plants and everything else being black, it just looks dead dramatic and it's not that hard to do!!
If (like me) your a bit rubbish with keeping plants alive then just do some experimenting, buy a load of different ones and see what takes off, you'll generally find one or two plants which work well so then just get quite a lot of them, you can do some really dramatic looking planting just using 1 or 2 species of plants.
often with decor like rocks and bogwood it's often a case of just hunting and hunting, just keep looking round all your LFS's each week and rummaging through the stuff they have and sooner or later you will find something that just jumps out at you as perfect.
we've been looking for some nice wood for months, finally found a nice piece a couple of weeks back...... now probably another 6 months looking for another piece to complement it! ha ha
a lot of the time i think it's simplicity which looks best, tanks with loads of different species of fish and loads of different colours and types of decor look tacky, stick to something like 3 species but get big groups of them and the same with the plants and other decor, use all the same types of rocks or wood and stuff. Just joins it all together nicely.