I feel like I'm starting to sound like a broken record here, but... buy and read Steve Blank's The Four Steps to the Epiphany. That's step one. Step two is "do what Steve says." Seriously, he lays out a very detailed methodology for going from "an idea" to "a validated and profitable market for your product." Note that he's only addressing the customer / market side though... You'll have to figure out how to get the product built. If you're a coder yourself, you can play both Customer Development and Product Development (that's what I'm doing, for example), or if you're not a coder (or just need more help) you have to start looking at how to acquire help with the coding side.