Your top banner is always the first thing your visitor will see and needs to give them a quick overview of your product and its benefits. Banners can be used smartly to convey the most important information that informs a visitor quickly so they decide whether to stay. Always keep in mind that what you think is important (as business owner) is not necessarily the same for the customer.
This banner example is a top banner for a newsletter, keep in mind that just because a visitor dropped into your site once they are not necessarily going to remember everything on your site. This example gives a quick reminder of the product and important links taking them directly to the site if they are ready to buy. Never leave a customer trying to find out where to go, if they have to think you will likely lose their order.