Do you mean an account profile or a Facebook page. Both should be run in a different way.

It depends on the product you are marketing, as well as your goals. Facebook can be used to share information - like business location, phone number, description, etc and/or it can be used for sharing deals and promotions with your followers and/or updating your clientele with current information.

Post your useful information or post comments on most relevant groups or pages. This helps you to bring more targeted traffic to your site that could be converted into sale.

First, you want to tell your friends about the product or thing your promoting. Then get them to share it. You can also try on some site that get you likes for the fan page, which will also grow awareness. Post messages on similar pages to yours advertising your product/thing. But dont spam whatever you do. Also use other social networking sites like Twitter to gain awareness of your fan page/product etc...