I think Rock1000 is right.
If breaking down into small pieces doesn't work for you, the best way is to set your timer for 15 minutes. You focus on your job and when the timer beeps, you take a break.
I really think that any task will take the time we have to allow to it. When I feel too lazy to clean my kitchen after dinner, I set my timer for 15 minutes. I always finish before it beeps. And then I am so proud of myself ! Even if I worked only for 15 minutes. (well, it is not like writing a thesis, I know, but a task we don't want to do makes us feel the same way, whatever it is)
Make sure you have all what you need to work, set your timer and Just Do It !
Another tip that works for me is to visualize and imagine what it will look like when I'll be finish and to feel how I'll feel.
Also, let go your perfectionism. You can do a really good job even if it's not perfect.
By working 15 minutes and taking a break 5 minutes, you will accumulate 45 minutes of good work during one hour. Set your timer for your breaks also. Do something you like, then say: Time to go back for another little 15 minutes !
Sometimes, I chat with my sisters and friends and we do that together. It is funny ! If you know someone who has a big job to do, you can work together. I say we work for 15 minutes, ready set go, and 15 minutes later we are back on MSN and write all we have done.
Well I hope this will help... Good luck from me too !