I like to apply a few different methods to developing web applications: I write unit tests to ensure the correct data comes out. This usually involves doing a

I like to apply a few different methods to developing web applications: I write unit tests to ensure the correct data comes out. This usually involves doing a quick "get a blank page loading" bit of boilerplate, then putting the tests (and required data) in place. This involves a fair bit of discussion, sitting down with a calculator, and drawing on the whiteboard. Then I write the code to pass the tests. In parallel, the screens are being designed and put up on our wiki. Once this is done, I'll make the screen look like the mock-up, which involves a visual "test". For more complex stuff, this is done in a more piecemeal fashion, although the design is usually put in place in one go. What I'm working on right now has involved 4 iterations of this so far. For what it's worth, writing the tests first forces you to make your code easier to test which, for a web app, is incredibly useful. I've seen some web applications developed without testing in mind, which tend to have the effect of "funnelling" the user through specific steps. They tend to get a little fragile when the user inevitably steps outside the narrow corridor they're pushed down.