When people move around frequently, it's easier to keep things pared down and organized, but when you have stayed put for several years, things do tend to accumulate! To keep the clutter to a minimum, a friend told me about her strategy: Pretend that you're moving out of each room, one at a time.
She said they had a rule that you took everything out of each room and you could only bring it back into the room if it had been actually touched and decided upon. They did this over a period of time, one room at a time. They could not just put a whole box back in the room; they had to go through every item in the box.
This approach might not work for everybody, but at the very least, do ask yourself these questions when you are doing an organizing project: "If I were moving, would I pack this item? Would I pay to move this item across the country?" It does make you think!