This is the Pomodoro Technique. There's a PDF (with productivity stuff, there's always a PDF) but the core idea's simple: set a timer for 25 minutes. Work without interruption until the timer goes off. No multitasking. If you get interrupted, start over. You'll be surprised what 25 minutes of focused attention will achieve.
Link to this | This doesn't fucking apply to me
You can buy the book on Amazon, but why bother? The PDF is free.