I have a friend, a writer I truly admire, Stephanie Bond, who gave a tip during a workshop to learn to write in small increments. She can set a timer and write for an hour or even 30 minutes, which means she is far more productive than I. I've tried this and I can even do it if I'm at the very end of a book, when every moment, sleeping and waking, is lived in the alternate reality of the novel's universe, and my own world is only viewed dimly through bewildered eyes.
But usually it takes at least an hour to read and re-read, to sit and dream, staring off into space, before I can fall into the place where the words come exactly as I want them. Well, never exactly, because there is always revising and rewriting, but closely enough that I'm satisfied with the words on the page.
Another technique many writers use is the crappy first draft, or don't-look-down first draft. Where you write anything, just to get it on the page, and then worry about revising later. I've never been able to do this, either. It paralyzes me. The Muse works differently in all of us; the Process is something that I've learned should be left alone. It's an arcane mystery in a world of pragmatism, at least for me, how this thing we call Creativity works.
So I let it be, unanalyzed, and try to be grateful that it works at all. Looking beneath the surface, trying to find the words.