SEE THE BIG PICTURE AND DON'T GET OBSESSED BY A SINGLE PIECE
Don't waste too much time on a single area or don't get obsessed by a single piece of the puzzle. Rather work on a different area or just go away, do something else and come back to the puzzle later!
Maybe you don't realize it at the beginning, but everything is connected. Working on a different area of the puzzle will sooner or later help you develop the difficult area as well.
And I can assure you that when you go away, disconnect and come back to the puzzle later on you will see things that you didn't notice before. That's because the brain kept processing while you were away or simply because before you were too tired or distracted to notice some details. I have experienced that so many times but it still amazes me how often it happens.