One word at a time. (I had writer's block answering this question)
Seriously, just write. Sometimes writing a story can actually bring out twists and turns that you don't expect. The characters may dictate how something happens or something else in that universe happens out of their control as well. That is when the story takes a whole different track (similar to how "One Man's Wife" changed on me while I wrote it).
"No More Goodbyes" was another one that took a different twist. I was thinking of making it a phantom hitch-hiker story but it became something else altogether.
Just do it (writing). If you type one sentence about how you feel, you have come close to breaking it than someone who looks at a blank page or screen and wallows in it.