Putting aquarium decoration has many benefits. Other than hiding unsightly aquarium equipments such as filter, heater, tubes from aquarium pump and wires, decoration also help to provide hiding place for certain fish like neon tetra which are rather shy. Putting backdrops could also enhance the beauty of the aquarium and they also simulate a more natural look. Fish also feel more secure as backdrops prevent reflection of the aquarium and exposure from all sides.
Other than that, go for objects which are easy to clean and maintain. One has to take into consideration that with decoration, comes more work especially when it involves routine work such as changing water and cleaning the aquarium. Avoid decoration which has narrow spots which can accumulate dirt and is potential breeding spots for bacterias which will cause problems related to aquarium fish disease.
Another important consideration aquarium owners should look into is that, try to avoid putting objects with sharp edges. Certain fish like the goldfish are rather clumsy and their style of swimming will cause them to bump into objects and get injured.
Certain objects like limestone and marbles can degrade and cause changes in water chemistry. The substance may slowly dissolve and alter the pH balance, so it's best to avoid using these as aquarium decorations.