I had a logic teacher in college who would force us to exercise this concept. He would have us look at the very last problem on an exam on test days and make us just stare at it (no working on it allowed) for 5 minutes. Then we had to start the test from the beginning.
The theory being that your subconscious is working out the problem and you'll have a better chance of figuring it out. I felt like it really did work.
Seems like he should've had half the class do the staring, the other half take the test normally, and give as many points as appropriate. One could get a lot of data after doing that for several classes.
He also liked to show off his many other amazing 'mind hacks' such as memorizing everyone's name within the first few minutes of the first day of class. There were almost 100 students in his class and after he said he was done 'doing his thing' he would ask the students to change seats and never sit in the same seat twice for the first week to test him.
The theory being that your subconscious is working out the problem and you'll have a better chance of figuring it out. I felt like it really did work.