1. When adding new species to your aquarium, you have to ease them in. Adding too many fish too quickly can cause the ammonia and chemical levels to raise quickly. Adding fish slowly gives your filter time to catch up.
2. Some people go by the ìinch of fish, gallon of water rule when deciding on how large of an aquarium to buy. This is a completely false and bad method to go by, you should always check your individual fish's tank requirements.
3. You should always thoroughly research the type of aquarium you are going to be setting up before you purchase it. Make sure you have the proper gallon capacity and shape that will fit in your home.