Think about the users that will use your app. Why are they using it and in which context?
- Will the majority be pro users that know the domain in which the application is used and use the app a lot? Then don't be afraid of adding a lot of data to the screens as long as it arranged logically for users (normally that is not in alphabetical order :-). Think trade screens for stock borkers or airplane cockpits.
- Are users occassional users? Keep it simple. Avoid context switches (keep all/as much as possible of necessary data for a task on the screen at each time). Don't break expectations of how gui widgets normally work. Design for failures.
- Anything in between? Allow users to grow in the UI. Track usage so you can later determine where users seem to spend the most time so you can improve the most used areas of your app.
- Test your app on friends and colleagues (the corridor test) to see if they are able to use it efficiently.
That's a start.
