Watch what you do: When you bring in mail, where does it go? When you see exactly how your clutter snowballs, you can get a better idea of how to stop it, Lark says. Could you stop at a recycle bin on your way from the mailbox to get rid of junk mail?
Name the problem. People often tell Lark, "I cleaned my desk, but it all came back." This language distances you from the real issue of what's going on in that space. "It" isn't the problem -- your habits are.
Set concrete limits. Saying "I'll buy less" is too vague. Better to say, "I'll limit my mess to these two rooms," Novack says.
Accept neatness as a lifelong issue for you. "It's a constant struggle, like losing 50 pounds and needing help to maintain it," Novack says. "You might gain 5 back and have to work hard not to gain 10 or 15."
Try formal help. Self-help groups like Clutterers Anonymous and Messies Anonymous give ongoing support. A pro organizer can help you get on top of things and learn ways to improve. Also useful are cognitive behavioral therapy and treatment of underlying issues, such as ADHD or depression.