When I was writing my book, I joined a writing class that gave us time to dedicate to our work. The first part of the day was for talking about our processes and then the rest of the day was dedicated to just . . . writing. Some people um'd and ah'd about what to write, but I quickly learned that I just needed to get going. The best lesson from this class was: there are no good first drafts.
If you are finally at the stage of putting some ideas down on paper, don't be intimidated. The first words you ever write will probably be long gone by the time you actually submit your application, but you have to start somewhere. Oftentimes, writing things down can help you think abut exactly what you want (and need) to say. It's a tool to clarify your thought processes.
In my office, I work with some extremely talented people. For weeks, even months, two of my colleagues have been brain-storming a management plan. They round and round, talking about the components and the structure and the desired outcome. This week, I had the pleasure of being asked my opinion on their process. "Just start writing it," I told them, "you have been thinking this thing to death and it's time to put it on paper." The next day, they started writing. At lunch, I asked how it was going. "It's almost too easy, I feel like we're leaving something out," they told me. I posed an alternative, "Or maybe all your planning and talking about it made it so that the work is actually done and all was left was to write it out."
If you're waiting until you have everything figured out to start writing, you'll be waiting forever. Sit your butt down and get a draft done. It'll be a start, but from there, you'll overcome the hurdle "starting" your application and coming back to revise your thoughts will be much easier. I promise. Give it a try.