When I hit a block and find myself staring at a million things to do or think or figure out, sometimes it helps to just try and encapsulate the things I can't do in some meaningful category. Then, if they sit there a bit, often one or more of them will sheepishly present a useful next step or next piece to be done. It's like, they love being all huge and unbounded — writing-projects especially — and therefore don't want to let me actually write words, because that will limit them. But then I put them down in just the few words that they are — the title, the synopsis — and stick all of that in a sad little shoebox, and when they realize I'm serious, one or more of them will say "Wait! We're also these paragraphs! And this character! Seriously, you can write this bit down too now…"
I find things like XMind(.net) helpful for this. I can poke at and stare at things like this one when I need to, and think saucily to myself, SEE? YOU STAY IN THE BOX UNTIL THERE ARE WORDS.