Banners are a great form of promotional advertising. You can utilize them as attention getters on other sites that viewers click on to bring them to your site to shop. They are also commonly used as banner exchanges in specialized programs that offer a 2 to 1 ratio. Meaning, each time 2 viewers visit your specially coded page on your site, your banner gets released to 1 viewer in the nation.
The key to a successful banner is to make the viewer want to click on the banner to see what you have to offer. Think of what makes you click a banner and then transpose that information to your own successful banner.