1. Top-level requirements: What problem or problems is this application going to solve, and for whom? If you can't answer these questions clearly, you aren't bu

1. Top-level requirements: What problem or problems is this application going to solve, and for whom? If you can't answer these questions clearly, you aren't building a serious application, you're just playing around. (This does not mean that you can't change your goals later, but you should always be building towards a clear, specific target.) 2. Functional requirements: What are the use cases, and how will the user interact with the application in each of them? Use storyboards, mock-ups, whatever helps you to understand what the application will do from the user's point of view. 3. High-level design: How will you model the data and functionality you've identified in the previous steps? Typically for a web app, a lot of this will be about setting up a data store server-side and figuring out how to implement any interactive behaviour client-side. You don't have to work out all the little details at this stage, but you need to choose a viable technology stack and know how the big picture is going to look. 4. Start prototyping: Set up the basics, enough to represent one key feature or perhaps a small group of related features, and create enough of the model/database behind the scenes to support it. Again, you don't have to code up every last bit of HTML and CSS at first, but you need to have a general idea of how things are going to fit together. 5. Refine what you've got and add further features and more details to the model, until you start to see how things are coming together. Go back often to check that the design and implementation are still meeting the requirements. Go back to the requirements themselves and make sure they are still appropriate as you gain experience in the field and/or you receive feedback from users/prospects. It's very trendy to just dive in at about step 4 and starting hacking away, at least among the young, entrepreneurial types who seem to dominate forums like HN. By all means try it: if nothing else, you will learn why steps 1-3 are important. Still, please don't bet your life savings on the project getting anywhere if you don't at least know where you think you're going before you start. You might well find that you change direction on the way, but aside from a few high profile exceptions, it is relatively rare in reality to see a successful business where someone just started coding something up one day and fluked their way into running a serious, profitable business before time and money ran out. Good ideas aren't worth much without a good implementation, but implementations aren't worth anything at all if they solve a problem no-one has.