I used to just wing my stories. I'd read the previous chapter before starting the next & just have at it when I was done. I'd have a general idea in mind, and it helped, but they turned out awful. I've looked back on it, and it really does look awful.

I started actually writing down stuff relevant to the story at least 2 or 3 years ago, and it helps a lot. I feel like I've improved a lot by having it written down and next to me when I'm writing so that I don't forget a detail or something while I'm writing.