Building, Shipping and Marketing SaaS Products
Product Design is an engineering process. It is not just about drawing a beautiful user interface, it is about building a solution to a user's need. It is a succession of logical steps in thinking and writing, which I recommend to browse through sequentially. And the best approach to my experience is going top down.
Products with uncontrolled technical debt are a pain as soon as you want to add or modify even the smallest feature. No matter how good they are, your developers will just struggle in getting your user stories "done".
This post is not about Agile. It is about getting things done. And it is about a process that serves business objectives. Understanding your context is key in selecting a methodology, so that you can then embrace it, and finally make it yours. In that specific order.
Christophe Dujarric 