Instead of writing a big to-do list and trying to get it all done, determine the 1-3 tasks that are absolutely essential and then focus on those tasks during the day. 

You don’t do anything else until you’ve completed the three essential tasks.

It's about working in short, productive, focused bursts, and then giving yourself a brief break. It only requires is a timer:

• Choose a task
• Set your timer for 25 minutes
• Work on the task until the timer ends
• Take a short break (around 5 minutes)
• Every 4 Pomodoro sessions, take a longer break (15-30 minutes).

Take full advantage of the energy peaks and troughs that occur throughout your day and correlate your maximum energy levels with your task list, which then gives your productivity a major boost: Work 90 minutes and then rest for 20-30 minutes. 

The human body operates on cycles called "ultradian rhythms." During each of these cycles, there is a peak when we are most energized and a trough when we are exhausted.