After having determined your customer and the problem you want to solve, you have to think about what jobs do your customers actually want to get done. Ask yourself the question: what are the tasks, the jobs that your target customer needs to do or wants to do to solve his problem?
Find a great problem worth solving and define its characteristics! Always remember: If there is no problem there is no business opportunity. Be critical about whether you address a marginal problem or a life-changing issue.