I have a few strategies; step away from the screen and go for a walk to clera my head and be in a different place to approach the answer. Sometimes settling down to sleep frees my conscious mind to let my subconscious have a stab at it. Often I've gotten a solution just before I drift off. It means I need to get up again to scribble the answer, but it's worth it. But often as as not it's just staring the screen into submission.