I recommend you take a look at Rob Walling's blog: <a href="http://www.softwarebyrob.com/" rel="nofollow">http://www.softwarebyrob.com/</a><p>He also runs the Microprenuer Academy that focuses on helping and promoting one-person startups. His key advice: focus on a niche industry or audience.<p>For example, a few years ago I had this great idea of building a task management app. I quickly discovered there were dozens of them, Asana, Producteev, Flow, Trello, etc. Using his advice, I could have focused developing a task app for a particular industry, say industrial engineers, architects, investment advisors, etc. His point being that specific industries have very specific needs, and one-size-fit-all, general purpose apps rarely targets those needs.<p>Bottom line, think about what kinds of app you'd enjoy building, social media, news, productivity app, game, whatever, then cross breed it with some underserved market.
Example: LinkedIn + Oil and Gas industry = oilpro.com