Have realistic expectations – and take a break

However focused you may be, setting the bar too high for what you can achieve in a day leads to frustration and feelings of inadequacy. Accept your (human) limitations and set realistic, achievable goals that support a sense of completion and achievement. Get clear on what you’re trying to achieve and assess whether this goal is sensible considering the day ahead. It may well be that you would need to break a big piece of work into smaller chunks. A completed chunck of work, even if small, makes us feel better and more motivated.
Lastly, the golden rule – take regular breaks. Realistically our maximum focus time is 4-7 hours, broken into 40-50 minute bits. The brain can only focus for so long without taking a break.
Recharge the concentration network of your brain
Giving your working memory a short break (including eyes off the screen) helps you stay alert and maintain your focus when you resume your work. Coffee breaks, a short walk, a couple of minutes of mindful breathing or gazing aimlessly into the horizon are all good examples.