Jason has a great post on THINKING. Which I discovered just now while I was procrastinating as I tried to avoid that very subject - or even as I was immersing myself in it. Not sure which. They tend to be the same thing with me.
You divide your brain up into parts and trick the smallest part into thinking it is actively engaged in something, while the rest of it mulls over stuff. And then suddenly the main part of the brain derails the smaller part, and you put down whatever crap you were distracting yourself with and THE WRITING starts to flow ... At the start of a project this is ideas and inspirations (which I have to write down quick before they vanish); and then later in the project the sieving, refining, focusing, initial plotting; then later again reworking, recombining, replotting, deleting, refocusing, and finally; I start the typing/scribbling part of the process, during which I usually go through all the previous stages several times AGAIN!
Which maybe is why it can take me FOREVER to actually complete a story*.
However when the characters start talking to you it can really speed all of this up, because you already have a 'lock' on the story, whether you realize it consciously or not.
*Or sometimes less than two months (for a two hour feature), start to finish, when the writing really takes over and your active brain has vanished into the mist of creation. And the majority of that two months is thinking time.
And now I must go write.