I get the whole fic written first before posting. That means a rough draft, and edited version, a typed version that gets a read-through, and then a pre-posting on a smaller site to get reviews that might point out something to change.
This is why I haven't posted anything in years. I'm stuck on the first phase for all my fics.
As for planning the story, I get a set of characters in my mind, and come up with an ending point I want them to reach. How they get there gets no prodding for me. I just observe them and write down what happens.