Design before code

I think it's useful to get people's reactions to your first design before you write the code. You're going to have to change more things when you write the code, but neither talking to people nor writing the code is sufficient on its own to find all of the problems. Waterfall is bad in that you're locking down the design too soon, and completely avoiding writing code before getting feedback means that you don't really know what the issues are, but the real point is that you want to overlap different stages, not that the rough order of stages wasn't right. My policy is that, at the first design meeting, you pretend you haven't written any code yet, and only admit it if someone notices that you seem to know too much about what's wrong with the simplest alternative design.