Single Best Productivity Tip?

Leo at Zenhaibits.net says it's to simplify and lists what the other productivity bloggers answered to the question. I would say for me it's either the capture (writing EVERYTHING down) but, more importantly, the review. What's the point of writing everything down if you don't review it, process it and check to see what's coming. As you get into this habit you will automatically begin to simplify because you will be able to decide what's most important to you and what you should be working on (or not working on) next.