The problem here is that you need some good user analysis and I'm guessing you've only done functional analysis.
Because your problem is so abstract, it's hard to give one good example of what you need to do. I'd go to usability.gov and check out the usability methods link, especially card sorting and contextual interviews.
Basically you want to do two things:
1- Discover where your users think how information is grouped on the page: This will help flesh out your functional requirements too. Once you've got information all grouped up, you've basically got your navigation metaphor set up. Also, you can continually do card sorting exercises right down to page and function levels - e.g. you do one card sorting session to understand user needs, then you take one group of cards and ask users to break that down into ranks of importance. Doing so will help you understand what needs to be in dominate areas of the screen and what can be hidden.
2- Understand what tools they already use: what they do and don't like about them. You need to get a list of tools/applications that they use externally and internally. Internally is probably the most important because there is a fair chance that most people in your business will share an experience of using it. External tools however might help give you context into how your users think.
Also, don't be afraid to get pencil and paper and sketch up ideas with users. People generally understand that sketches are a quick and useful way to help with early design work and you can get an immense amount of information out of them with just simple sketches. Yes, even do this if you suck at sketching - chances are it won't matter. In fact, crappy sketches could even work in your favour because then nobody is going to argue if buttons should be blue, red or whatever.