Rescale your expectations/plans/schedule such that shipping is easier than not shipping.
My business started with an 8 day deadline, largely because I thought if it was longer it would end like all of my other private projects, with several months spent on research, filling out notebooks, and grand plans followed by a failure to follow through. I figured if it was just 8 days that it would be easier to finish rather than telling Dad et al "Yep, that ended up not going anywhere".
Make a list before starting. Break it down into small tasks. Or at the very least break the overwhelming task down into smaller milestones, set deadlines for those, plan the living daylights out of the first milestone, get started, and repeat.
(I wonder if I still have Matt Groening's Life in Hell cartoon about grad school, in which he describes this sentence as an all-purpose recipe for avoiding working on your thesis.)
