Thats the core of the Lean Startup. You start with your customer and the job your product is going to do for them. Does it solve a problem for them? Engage a passion? Develop your ideas about this (your Hypotheses) and test them. Keep at it, learning each time around, until you have a minimal product that is a viable solution for those customers — the Minimum Viable Product, or MVP.
I like the approach taught in the LUXr Bento Series, a set of workshop boxes that teach a user-experience based approach to Lean Startup. It’s methodical and incorporates tools that promote good team dynamics and clear thinking. This method is taught at some of the premier startup incubators and in my workshops. You can also now get the program directly from LUXr