I like the Pomodoro method. Basically, focus on a task for 25 minutes, then take a 5 minute break. Every 4 blocks, take a 15 minute break instead.

I work at home, so I do housework in some of those 5 minute breaks. It's different enough that it helps clear my mind enough to focus again after the break.

I'm still trying to find a good way to plan these work chunks, but so far I think emacs org-mode will work pretty well.