There's a story about Thomas Edison that has made quite an impression on me.
There was a mathematician who had the job of figuring out the volume of the lightbulb. Since it was an unusual shape, neither a sphere nor a cylinder, this wasn't an easy proposition. This man was very intelligent and well-educated, and he went about his task very conscientiously. According to the story, he consulted all his textbooks, he tried different formulas, he consulted all of his professors, and he consulted his professors' professors.
The mathematician was hard at work when Thomas Edison came in from a walk and said, 'You know, it's beautiful out there.' And the mathematician was thinking, Well, great; you're out taking a walk while I'm sitting here breaking my pencils working on this.
Edison continued, 'You know, I noticed this lovely pine tree. Did you ever notice that pine cones grow upside down?' Edison went to pour himself a glass of water, but instead of using a glass, he walked to the mathematician's desk, picked up the lightbulb, turned it upside down, and poured the water into it. He then handed it back to the mathematician and said, 'Here, measure the volume of the water.'
With any problem, I always advise people to turn it upside down. Look around you; get inspiration from nature; go for a walk; go outside. Don't just look at the task at hand.