It really depends on what tank styles you like, but I suppose some very general guidelines would be: tall plants go into the background, medium plants into the midground, and short plants into the foreground - this gives an impression of depth. The more the varieties of plants, the better. Various rocks and driftwood in similar color to the gravel also look nice in a planted tank. But there are also setups that do not involve plants. If you want some great ideas on how to aquascape a variety of tanks (planted and non-planted), I recommend for you to read Peter Hiscock's "Aquarium Designs Inspired by Nature". He gives a lot of ideas and instructions on how to aquascape according to specific biotopes. If you want a great book on planted tanks, Takashi Amano is the man. His tanks are breathtaking. I have his "Nature Aquarium World (Book 1)" and there are a variety of beautifully planted tanks as well as great tips on how to create such tanks.
Thankyou for you idea Isabella.
I'll keep an eye out for those books, (both sound very interesting) and I might have a look through the forum pictures to get an idea of the sort of decoration I like!
I'm not sure about you, but driftwood is stunning. I really like it because not two pieces are the same (if you get what I mean!) and it really gives it that natural look that I'm after.
BTW: The fish tank I'm going to get is about 50 Gallons, and I'm 'over' the plastic replica ideas, infact... I might try to keep some live plants too!