Predict what the user wants to know, and give them that information.
Information must be easy to find.
Your UI should be easy to use and navigate. Use established patterns where you can: Everyone knows that Ctrl-Click adds items to the selection, so don't make it swap items instead.
Make the user's location in the menu system obvious, and make it obvious where the user can go and what they can do from there.
Minimise load times and avoid animations in your menus.
Eliminate or simplify repetitive tasks.