Making a thesis plan has undoubtedly been the most useful thing I've done in terms of writing up. It's rather, er... organic, and subject to change at a moments notice, but has been a sound basis for all my chapters thus far. I'm writing a science thesis, and I organised it from the middle outwards; 4 structured 'results' chapters, an analytical techniques chapter; an introduction and a discussion. I found it useful to make a master folder, 'PhD thesis' or something equally imaginative, then made 7 folders within that. Into each folder I moved all the relevant electronic papers and absolutely anything I'd ever written and any diagrams I'd made that were even vaguely related. By the end of an afternoon I had a (very skeletal) outline of a thesis! Try it, it really works, and is a great confidence booster.