Every article should be well written, engaging, and informative. If at all possible, it should present a new angle on a specific topic, provide a good hook in the beginning so people will want to read on, and contain information that is in some way important to your readers. This can mean that it's useful, entertaining, or otherwise valuable.
A well-written article with good content will attract more traffic, which means readers that visit your site. This will make it more attractive to link marketers (people that link their sites to yours) and increase the likelihood of advertisers wanting to use your page for their advertisements.