Leo Widrich shares many strategies to increasing our creativity in his article, Why we have our best ideas in the shower: The science of creativity (thanks, Titania Richard).
While there is lots to like about that article, Harvard researcher Shelly Carson mentioned one thing that I have said repeatedly here (1, 2, 3, 4):
“a distraction may provide the break you need to disengage from a fixation on the ineffective solution.”
Fixating on problems leaves no mental cycles left for solutions. Learn to recognize when your focus on a problem is becoming a hindrance to getting a solution. Find a way to take your mind off of the problem. Releasing this mental pressure creates the vacuum necessary for a solution to enter.