The current issue of Mslexia has some tips from journalist & novelist Aminatta Forna. They're all good advice, but I particularly liked this one:
When you get stuck, it can be quite useful to go back and work on what you've already written. Perhaps the story has slightly changed since you wrote that chapter? 'Housekeeping' work - revisiting, editing - keeps you going with the flow.
This isn't advice you see very often. More usually, you're told as a writer that going back and editing something stops the flow and is therefore a Bad Thing. But this sounds very sensible, and I've done it myself a few times and found it worked. I just have to be careful not to get so bogged down in the minutiae of whether it should be 'and' or 'but' that I lose track of the story entirely!