The best way to write your proposal and dissertation is to block out times during the day specifically reserved for writing. You can’t write something this large and involved by writing fifteen minutes here and another thirty minutes there. Novelists and playwrights don’t write that way, and neither should you.
Make an appointment with yourself to write. Don’t wait for inspiration. Of course, that doesn’t mean you should ignore those moments when inspiration strikes. It’s always helpful to have some paper and a pencil handy so that you can write things down as you think of them. Don’t rely on your memory because you may easily forget later. I used to lay awake at night thinking about things before I fell asleep. Sometimes, those moments of inspiration come when you are actually in front of your computer, working on your manuscript. Those are the best moments—when the words fly out of your head faster than you can type them, and the manuscript seems to just write itself. Admittedly, those moments are rare. Most of the time, writing is work, and good writing takes time; so don’t rely on inspiration to get you through your proposal and dissertation.
When you’re writing, don’t let things (or other people) become distractions. Admittedly, this is hard to do at times. You’d be surprised at how easy your mind can start to wander. One minute you’re having a great thought about existentialism, and the next minute you’re wondering how to get the phone number of the blonde girl in your existentialism class. I’ve met countless students who’ve had terrible trouble motivating themselves to write ad get their thoughts onto the page. However, if you force yourself to write, preferably at the same time every day, it’ll become easier as you train yourself to “turn on” your writing skills on a regular basis. Treat the dissertation as you would your job, but treat it as though it’s your muse, too. And think of yourself as a writer. Keeping ideas in your head doesn’t make you a writer; writing does.
If you have trouble writing full paragraphs or even full sentences that articulate your thoughts, then start with your notes. Spend time taking notes on the literature you’ve read and try connecting those notes together. You can always create full sentences and paragraphs later. The important thing is to get some of your initial thoughts down on paper or imputed in the computer, no matter how rough or inarticulate they may sound at first.