I have far more experience with writer's block as an arranger and songwriter than I do as an essayist/author, but my process is the same. If I'm stuck in the chorus, I jump to another part of the song. I write the parts I know, I answer the questions I can answer. Then, once I've gained momentum in the easy sections I'm usually much more able to go back to the section that gave me trouble and work through it.
In fact my 10 step arranging process follows this same formula: answer the big questions first, frame everything out, decide what goes where, then the detail work - the actual writing - is far easier because you're focused on one small piece of work.