When you first set up your aquarium, don't make every beginner's mistake and set it up by a sunny window so that your fish can have a nice view. Excessive light can cause unsightly algae in the aquarium to grow like crazy. Stay away from fluorescent lights, too, as they can also breed algae.
Choose a dark, quiet place for your tank and ask your sales clerk about which light is best for you to use.
For more information, please read the story Setting Up Your Aquarium.