How do you write?

So, I have a file sitting on my computer, entitled 'Big Bang notes' into which, currently, everything I'm thinking about for this story is being shoved. It's a better way of keeping things together than endless post-it notes, which is how I organised my entire working life when I was working somewhere that I had a desk.

Currently, the contents of this file are about half a page of A4, and there is one thing that is actualy a major plot point. It's three words: search for Elizabeth?

Everything else is notes for little moments that I'd like to have in the story; some of them are tiny ideas, like 'Cam having a this is so cool moment' and 'Lorne with Parrish and Cadman, being teased for something really embarrassing that's happened recently'; some of them are actually vaguely related to plot, like 'Cam and Rodney get stuck somewhere to make it up' (because hell no are they going to get along in the beginning) and 'Cam sent to Atlantis because of injury?' (because, really, wouldn't Daniel be a much better choice?).

There's also half a dozen or so lines of a fight between John and Rodney, because even I in my happy John/Cam OTP land think that John's feelings for Rodney by season 4 aren't just friendship. Actually, this scene has been bouncing round in my head all week.

I still don't have an actual plot, but I figure I'm going to go with my tried and true method of plotting, which is to say, start it and the plot will develop as I go along. Plotting everything out beforehand bores me to tears, to be honest, because I feel like I'm just writing up what I already know, and there are no surprises.

I've been reading a lot of posts about people plotting out their stories by chapter, or by main plot points, or even just knowing most of what's going to happen, though, and I'm kind of curious about this. How do you know what's going to happen? Does the plot come to you pretty much fully-formed, or do you develop it as you write your notes or what? Explain this mysterious method of plotting to me! I don't get it!

Also - do you make notes for other stuff as you go along? Every story I've ever written has had a page at the bottom as I've gone along where I've stuck ideas for what will come next, and bits of dialogue, or description that I'm thinking of using, and sometimes even the end line (not always - more often than not, I'm writing away happily and suddenly realise, huh, that's the end and I have nothing else to say). Do you do that? Do you find yourself walking around with your main characters playing out a scene you haven't written yet in your head? Do you wake up with a brilliant idea for what comes next, or find yourself jotting ideas in the margins of your lecture notes? If you make notes, what kind of things go into them? Do you usually use everything that you jot down or does some of it never happen? Does your plot ever get derailed partway through, or are you stronger than that and keep it going where you originally intended? What makes the difference?

If you're anything like me, you love to talk about how you write, how you plot, why you do it that way... so come tell me!