Chief Creative Officer at Ideo Paul Bennett, in The New York Times:

Creative people thrive on serendipity, spontaneous interactions, moments of ribald humor, intense debate or just simple eye contact, and I felt as if I was losing myself. I decided that it was time to act. So I tried an experiment. I just stopped saying yes and started saying no to things.

Actually, there was a bit more method to my madness. I started a ritual that I still use today: I sit down and look at my calendar every Sunday night, pore through my coming week’s meetings and cancel a bunch of them — redundant ones where I don’t need to be “in the loop,” ones where there is an opportunity for someone else to make a decision, ones that don’t particularly inspire me, or ones where I can’t really add value. My overarching goal right now, wherever possible, is to give myself more time to simply be.

I have a similar ritual on Sundays as I prepare for the week and I make as many decisions as I possibly can for the week on Sunday so I don't have to think of the day-to-day and can focus my attention on relevant details. And speaking of details, don't miss an early TED Talk by Bennett on the small details.