One of the ways we've done this is too get rid of a lot of things by giving them away or throwing them away.
Another way we've worked on this issue is by setting up a "confiscation bin." It's not the most creative title but it does work.
The rules are simple.
1. Do not leave your things lying around.
2. If you do leave your things lying around another family member can pick them up and put them in the confiscation bin.
3. Mom and Dad are not exempt.
4. To redeem an item from the confiscation bin the owner must first complete a job from the job jar.
The job jar has a variety of jobs that need to be done from time to time but do not always get done in the day to day routine. Things like "clean under the living room couch" or "wash windows in upstairs hallway."
While we all have found our things in the confiscation bin (notice my shoes that I kicked off after church Sunday now waiting redemption in the bin) it has greatly reduced our quantity of clutter.
And, as I'm sure you can imagine, the kids get a great delight out of finding things that belong to one of the adults and making a big deal out of confiscating it. But we get a good laugh, acknowledge we're human too, and pick a job from the job jar.
It works for us.