1. It is generally a good practice to purchase the largest aquarium that you can actually afford. A larger aquarium will be less susceptible to quick changes in the chemistry, and will offer much more stability.
2. 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.
3. It is a good idea to clean your aquarium with a soft wash cloth and warm water. The soft cloth will not leave scratches on the inside of your aquarium and will remove any unsightly stains.