If there is one thing I've learned about being a designer, it's knowing when to take breaks. Stepping away from your work for a bit is always a helpful tactic, even if you think you're on the right track. When you're staring at a computer screen for hours, eventually you're going to become blind to the faults of your work.
Taking regular breaks from sitting at a desk has many health benefits, so this should provide the perfect opportunity to get away from your work for a few minutes. Grab a coffee/tea, take a quick walk outside, whatever your work environment enables you to do. Just get whatever you're working on out of your head for a few minutes.
I find when I come back from one of these breaks it's easier to notice little problems with color, type, alignment, or maybe a typo or 2. Sometimes I'll think of a solution to a problem I'm trying to solve, and I'll wonder why I didn't think of it before.
It's easy to get caught up in producing pixels, but the whole process is what design is really about. Pixels are just what make up the final result. It may sound counter-intuitive, but taking a few minutes away from design can actually be one of the most helpful tools.