Reading widely (i.e. not just technology blogs/forums), being genuinely interested in what other people do and the problems they experience in doing such things, dissecting a problem to see whether it can be avoided or ameliorated, exploring existing attempts to do so, analysing their benefits and failings, developing an alternative approach to the problem, discussing this with people I trust who have different knowledge-bases (particularly if they have knowledge of this area), reflecting on whether it still seems like a good idea, doing some rough calculations about market size, pricing (or other monetization route), and feasibility given my own skills and network, concluding whether it is a good and implementable idea and, if so, getting to work and continuing to work long after the initial excitement wears off.

tl;dr: Assuming until proven otherwise that everyone has something to teach me about the world.