Evan Williams of Twitter offers a structured way to evaluate new product ideas based on seven factors: tractability, obviousness, depth, wideness, discoverability, financial viability, and “is it personally compelling to use?”
Everything is obvious once its successful. Big wins come when you can spot something before its obvious to everyone else. There are several vectors to this: 1) Is it obvious why people should use it? 2) Is it obvious how to use? 3) Is it an obviously good business?
A structured method like this one helps keep emotion from dominating the process (just wanting to build something can distract you from evaluating it objectively), and let the natural tension between factors like obviousness and tractability help you decide not only whether the idea is basically sound, but whether it’s worthwhile for you to pursue.