1. Try to provide an environment that is as stable as possible, fluctuations in the aquarium can have a negative impact on the aquarium. Try to keep the temperature and PH levels fairly balanced in your aquarium.
2. It is a good idea to keep carbon on hand in case of emergencies. Carbon can be used to soak up anything harmful that may be introduced into your aquarium. So keeping an emergency stock can be a life saver.
3. It is not considered a good idea to keep aggressive fish with fish of other temperaments. You should keep peaceful fish in an aquarium with other peaceful fish to avoid any sort of fighting between the fish. Aggressive fish should only be kept with other aggressive fish.