The amount of contents that feel comfortable versus "overstuffed" varies as a matter of individual and cultural preference. For instance in the Victorian upper class, knickknacks on all available surfaces were stylish. See the article on clutter for other examples. Once you've come to some consensus about which things are clutter (as opposed to useful or beautiful objects that are where they belong), then you can begin to get rid of the things you don't want at all, and to find places for the "good stuff" to belong. Decluttering is part of many cleaning and organizing strategies.