I have in my life been guilty (ahem) of being cluttered, both mentally and organizationally. In the interest of minimizing the former, I've adopted some strategies for dealing with the massive flow of information and actionable tasks that come my way each day.
One controversial strategy of mine is to maintain an empty Outlook in-box, a Getting Things Done lesson if ever there was one. People I Have Known have at times been almost proud to tell me how many unread emails were in their in-boxes. One record-holder would auto-delete anything unread that was over 30 days. My take is that if someone sent it to me, there might be something in it of value. Best to find out sooner rather than later.
But the strategy that sprang from this that I find most appealing - and so far most challenging - is to avoid creating a stack of anything on my desk.
Put simply, the rule works like this: No item may be placed on any other item.
Given that I have limited real estate on my desk, and given that I know OOS=OOM (out of sight equals out of mind), this forces me to make some hard choices on a constant basis about What I am Doing Now, What I Am Doing Next. To say nothing of Later or Never.
It's strangely calming. Try it and let me know what you think.