Your "how" sounds a lot like mine -- write down the bits as they come, which are often the dialogue first, and join them up however it seems to make sense. Which is why I almost never know how long something is going to be until it's actually finished... Aside from oneshots, which are generally under 5k, I've only managed to sit on two chaptered fics until they were finished to start posting them, one because it was for a big bang and one because it was a spoiler for a current WIP storyline that hadn't come to that part yet. (Oddly enough, they're both about 17k words, as it happens.) And then there was The Werewolf Story, which I thought was only going to be the drabble that's now chapter 1 until the backstory grabbed me and wouldn't let go; surprisingly enough, I did work out around chapter 4 of that that I was going to have 13 chapters of material for it and was able to plan that out accordingly. Obviously this isn't the sort of process that lends itself to formal outlining, or even conventional betaing... (the big bang required going through beta, which is actually the first time I've used one for my fic, and neither of mine found any major issues by the time it got to their hands 'cos I'm already paranoid about proofreading the hell out of my stuff ;) )