Set a timer for twenty-five minutes and concentrate on one particular task. When the timer goes off, take a break for five minutes (setting the timer for it) and do something else: check social media, respond to a few emails, take a short walk, or do a quick meditation.
After your break, re-set the time for twenty-five minutes and resume concentration.
There are various Pomodoro Timers you can find online, including physical timers. You can even use the timer on your phone or a kitchen timer—pick the one that works for you.