An artist I knew sometime back would always work on multiple artworks simultaneously. He would tell me that in his break from one painting he would work on the other, allow it to physically dry and perceptually harden in his mind.
When we work on a particular task there is a set amount of neuronal activity that is taking place and a bunch of neurons lighting up in our brains. Our feeling of getting stuck is probably our need and inability to move beyond this set bunch. Thats where breaks come into picture.
A break need not be whiling away time or sitting empty. Most times the best breaks are the ones that include set tasks as they take you a good distance away from your primary task and engulf you into a new world of neurons somewhere far away. Picking up that guitar, organizing a small corner of your room, tending to your plants, etc. can feel much more rejuvenating as such. One can even pick up a mundane task that requires less effort to be executed in a break. (Probably something my artist friend would do)
The idea is to engulf yourself in another world without draining your energies down so that you can return to your primary task rejuvenated.