1. You should always research the different types of fish you are going to be housing together. Certain fish can be extremely aggressive and cannot be paired with other fish of different temperaments.
2. It is important to pay attention to the limitations of the fish you place in the aquarium. Do not place fish into aquariums smaller than there recommended range, this can lead to increased aggression and decreased health.
3. Provide plenty of places for your aquarium animals to hide. Studies have actually shown that the more places a fish has to hide, the less likely they are to do so! Hiding spots also provide safe spots of refuge for smaller fish in the aquarium