Disconnect from distractions. Get that mental energy pumped up.
Have you watched any Tony Robbin videos on youtube or been to his seminars? Maybe tried working for a marketing firm? Or worked a job with inspirational pre-work meetings?
What I remember from what these have in common, is they take time at the start to get juiced about working. Typically involving a little chant. Often accompanied by some music. Together, they start to get you energized. In which you end it, by yelling atop your lungs.
I don't usually need to go to such lengths. But, when I have project with a due date - I set up a playlist of inspirational music videos to start off with before writing. Or, I might play The Secret recording. Or, watch a Tony Robbins video. Any of them work. Generally, it's what inspires and energizes you to push yourself to succeed.
Music during writing can also help keep energy levels up as well.
But to truly make it work, discipline is needed. You set yourself goals. And find ways to get energized. Setting up a reward for yourself for meeting writing quotas (goals) is also important. But, don't allow yourself to quit till you meet your set daily goals. Otherwise, you don't get the reward for the day and/or pay a higher price that acts as deterrent.
A major deterrent you could do is force yourself to pay out a large amount of money to an organization you dislike if you fail to meet all your goals. Then write a reminder, and then you'll know you need to stay on track. That is one idea as well for a form of self punishment for not meeting a goal. With this as a deterrent, it could help you stay on track. Of course, if you do this you should also offer yourself a sweet reward for success when you meet all your goals.
Or sometimes, working on one project too long can be a de-motivator. In which case, simply switching to a different project can be a big help. It's mentally refreshing, and will help re-energize the writer in you. After all, you can always tackle the old project again in the future.
Well, I hope that helps. Good luck. ^^