A mention of the Pomodoro technique is relevant. It encourages 100% focus on work for 25 minutes followed by a 5 minute break where you are forbidden to work at all in any way. You're supposed to tell a joke, stretch, stare out the window, etc. But no meetings, no email, etc. At first I felt a strong resistance to the "stop work" part, often delaying until "one last thing" was done, but I tried it anyway. What surprised me was that without exception, my thoughts and actions were clearer when I took the break. It never really added a delay, and in fact sped me up considerably. I'm not entirely sure why, or whether its true for others, but that disciplined cadence of 25m 100% focus and 5m 0% focus is like magic.