On a basic level, useful content solves problems, satisfies reader needs and adds value. So your content could be a tutorial; a revealing interview; a first-run news article; or perhaps a list of handy resources.
As Jesse James Garrett” writes in ‘The Elements of User Experience': “The single most important thing most web sites can offer to their users is content that those users will find valuable.”
Of course, the definition of ‘valuable’ varies. Often wildly. An article like “Why Microsoft has made developers horrified about coding for Windows 8″ might catch your eye. Or you might be tempted to click a headline like “How to Lose Weight at Work.”
Ultimately, you’re going to need to develop an understanding of who your readers are and what they want. You’ll need to test and tweak your strategy until you find the content and the presentational elements that work best.