Work on a task for 25 minutes (a “pomodoro”) and then take a break for 5 minutes. Every four pomodoros, take a longer break.
Like the book proposes, I am using a kitchen timer (I did so after reading Lakein’s book back in 2008). Besides using hardware, there exist a number of software packages that countdown from 25 minutes. I think however, that that following shell script is among the simplest (if not the simplest) implementations:
#!/bin/sh ( sleep 1500 && xlock ) &
( Tested on OpenBSD-4.7 )