Time off is good for this - for example, when writing, I often set drafts aside for a few days before rewriting.
Maybe closely examining a similar product with a different interface would help?
Or maybe trying to mock up a design how you imagine someone else would do it? Perhaps a competitor?
The guy who taught me how to eat sushi a couple months ago explained that I should get a slice of ginger before trying a different kind of sushi in order to "reset my taste buds" (probably broscience) and feel the taste anew (it works). That's also the exact problem that programmers face when trying to design user interfaces: after looking at the thing for a long time, they grow blind to its shortcomings. A visual reset would come in handy. I imagine that resets could help in other areas too. Does anything like that exist? Cogsci majors, help!