One thing a friend of mind did during their PhD which he said was very useful was to always have his thesis. Every month he took a few days and wrote up his current state of mind and conclusions were. So over a period of years he went from rough outline to final thesis without ever having that 'OMG got to write everything up' moment. It also have him a lot of practice writing. Yeah — he ended up throwing away and backtracking a few times — but he was so chilled compared to his peers when it got to the end of his doctorate.

(and by curious coincidence one of the authors of this piece, Ben du Boulay used to be my boss many moons ago ;-)