A strategy that occasionally works for me is to start the thing with no intention of following through. Just give yourself permission to give up after some negligible effort, no matter how inconsequential. For example, just tell yourself you're going to pull out the assignment and arrange it on your desk and that's it. Or you'll just load the project in your IDE but not commit to any actual work.

When I do that, it sometimes gives me enough inertia to move on to the next step.