I think it's just a matter of one step at a time. I would make myself a little timetable (perhaps it was a way of procrastinating??) with mini steps to complete to get the assignment done. I'd sometimes even give myself an aim, such as complete 200 words a day, making sure I allow a couple of days at the end for editing and proof reading. I found the '200 a day' worked well when I was really unmotivated as only 200 is easy. I could 'cheat' some days by maybe writing the opening of a few paragraphs that I knew I wanted to write (but couldn't be bothered looking up facts for at that time) and on other days, when I was more motivated I'd do the more nitty gritty stuff.

Oh a side note, I'm a teacher who recently did my Masters, so I'm still pretty fresh with the study thing. If you'd like some sort of help so you pass the topic let me know. I can't promise anything, but I'll do my best!