1. You should keep the temperature in your aquarium constant. Constant change in the aquarium can be dangerous for the fish in your aquarium. Keep a quality heater and accurate thermometer to ensure that the water stays stable for the aquarium.
2. When adding plants to the aquarium, be sure to check the lighting needs. Try to find plants that will fit the pre-existing lighting conditions of your aquarium. You should avoid plants that require much more light than the fish in your aquarium.
3. When adding particularly aggressive fish to your aquarium, it is a good idea to move around the rocks and such in the aquarium before placing the new fish into the aquarium. Moving the rocks in the aquarium will allow the fish to go back and stake out their own territory.