Design the top level of your navigation in isolation. Base it on your top 20 tasks. Then test it with about 20 top task questions. Ask a minimum of 20 people what their first click would be based on the navigation you present them. You can do this manually using the simplest of wireframes.
Aim for a 90 percent first click success rate. Keep tweaking your navigation until you get that success rate…
Most of what you will be doing to improve success rate will involve changing words.”