I take a small break (15 mins) and then either find the motivation to continue onto another big task or work on polishing the "small things" that always pile up

I take a small break (15 mins) and then either find the motivation to continue onto another big task or work on polishing the "small things" that always pile up. While the break does it for me, the important part is that you reward yourself in some way immediately after to engage the "work-reward" cycle.