The most common mistake we find writers making, albeit with the best of intentions, is to open their novels with some kind of information—exposition—rather than with a scene, something that happens. (Or by pulling the reader’s attention from an opening scene to explain it in some fashion.)
This is often deliberate, the idea being that the more readers know about someone or something, the more likely they are to take an interest. But most readers are more inclined to take an interest in a story based on witnessing what characters do, say, and think than on what the writer tells them before they have a chance to see the characters in action. This is just one reason why it’s a good idea to begin with a scene, or a character facing a challenge. It’s also the principle underlying the most time-honored advice for the novice fiction writer: show, don’t tell.