I usually create outlines of sorts. I write notes about which things need to be included, and then I work from point A to point B to point C and so on. Every few points, I re-read my writing to make sure I am accomplishing what I set out to do, and I fill in information I have learned about my characters or the story from writing more. I usually re-read a chapter (or about a few thousand words), make sure it's okay, and move on. After a few chapters, I'll read all the writing at once, again making sure my story fits the vision I had for it. I edit out discrepancies and information that is no longer true or correct. I find typos. Once that part of the story is complete, I leave it at that. Then I do the same for the next part and the final part. Lastly, I'll read the entire piece at once in a couple weeks (when I can no longer guess words before they come up, and I have a clear mind). I add in special details like foreshadowing or secret hints, or I improve on the suspense building or character development.
To me, writing is the process of slowly weaving a story together. Editing and revisiting the story are two important things.
If I want to just write something, anything at all with no goal, I use writeordie.com, or I wait until I am actually inspired by something. It's hard to write a creative piece in a sincere voice when I don't have the passion for it. I have to want to know how the story ends.