When I cannot concentrate on something, I usually change my occupation (I go for a walk, for example). And if this happens systematically, then there is a problem in the work of the brain, you need a healthier diet and lifestyle in general.
Mine ?i just take a Nap when time that i felt like my mind is too full to accumulate more ideas.
And it helps a lot , I even find my self open for more and more things whenever there is a rest that i got.
Try to nap even when you are in office for at least 5-10 mins that is more enough to restore our mind freshness.