Build tools, not instruction manuals.

Think about paths instead of hierarchies:
A great post by Ryan over at 37Signals. He offers a way into the design process that makes a lot of sense to me, a way-in that I am printing out right now and taping to the wall beside my computer. He writes:

Instead of thinking in terms of hierarchy or up-front structure, I think it’s better to work with paths. A path is a line that goes from a starting point A to an accomplishment B. Each customer who comes to the site doesn’t care about the overall structure. They care about getting from A to B. That’s a path. Where are your golf shoes? That’s a path. Does my cell phone support international calling? That’s a path. Collect all the paths you can think of in a pile, pull out the 8 paths that 80% of your visitors come looking for, and that’s your home page. When paths overlap or the same customer needs them, weave them together. Add the occasional fork.

Using this approach, you turn your design into a tool, something to be used. Starting with a hierarchy of information - say, like, trying to distill the three main categories of your client's business and building a nav bar around that (which is how I've designed pretty much every site I've ever worked on) - leads to a site that is, most usually, a great hierarchy of information, but kind of a crappy tool; like trying to convince people that the instruction manual is the tool.

(Via Signal vs. Noise.)