1. Having a quarantine tank on hand is a very good practice to use if you frequently buy new fish. The quarantine tank will weed out any sick fish that could possible get into your aquarium and cause harm to the other inhabitants.
2. Only use medication in your aquarium when you are out of other options. You should use a separate tank to medicate sick fish as some medications can have harmful effects on healthy fish.
3. It is good to budget out the cost of your aquarium. You should leave plenty of money to purchase quality filters, pumps, and heaters for your aquarium. Your big aquarium is going to do you no good if you do not have the proper equipment to keep it going.