Wil Wheaton recently had an insight about writing:
"I made two huge mistakes with that," I said. "First, I didn't realize until I was almost ten thousand words into it that it can't be a first person narrative, because it's way too limiting for what the story needs. Second, I didn't outline it before hand, I just had a basic idea for where I wanted it to go, and tried to write it by the seat of my pants. It was really stupid to do it that way, but I learned a valuable lesson from the experience: I need to work from an outline, because when I do, I'm connecting the dots instead of assembling a jigsaw puzzle."
I work from an outline, so this seems really obvious to me. Put together the general structure, spot any obvious dead ends, then skip around writing scenes to fill in the gaps. I know other people just start at page 1 and go where the story takes them, but unless I have some kind of sense of the destination, I would find that very difficult. Sometimes I have a formal outline with chapter headings, other times just a couple of pages to tell the bare bones of the story.
After writing it, I go back and try to see what worked and (despite best intentions) what didn't. Changing some major facet after having written 10K or 50K (the POV, the setting, the fundamental relationships) would be work, and lots more work afterwards to make the work work, so to speak. Like converting a gasoline engine to propane. First, you work like hell to make it run at all. Then, you keep working to get it to run well. Daunting, but not impossible.
Blog posts can be seat-of-the-pants, because they are rarely more than a couple of thousand words, and rarely express more than one or two major themes. There's no story arc in a blog post.