George Heilmer (somewhat) famously proposed a list of questions that you should be able to answer before starting any new research or development project:
What are you trying to do? Articulate your objectives using absolutely no jargon. How is it done today, and what are the limits of current practice? What’s new in your approach and why do you think it will be successful? Who cares? If you’re successful, what difference will it make? What are the risks and the payoffs? How much will it cost? How long will it take? What are the midterm and final “exams” to check for success?
Every second year graduate student should have a worksheet containing this list as they prepare to propose their thesis project. It’s equally applicable to grant applications, product design in industry – damn near everything you do in science really.