First, I get an idea. It could come from something as small as a comment a friend makes or something I see on TV or even something I think of while working on school.
Next, I'll write down the idea. I'll generally do this in one of three pages in my iPad Notes app, or, if I don't have access to my iPad, I'll scribble it down on some nearby paper.
The next step varies. If I'm working on enough stories at the moment, I'll just write down as much relevant information as possible and store it for later (this is something I've gotten better at; I used to just start working on a book as soon as I got the idea). However, if I don't have too many projects already, I'll start working on the book immediately.
After that, I generally like to plan out the main characters. The protagonist, the antagonist, the best friends, the parents, the love interest, etc. They often don't always end up like I plan them to (there's a guy in Teen Author who was originally supposed to be the love interest, but then things went another direction and there's an entirely different love interest...), but it's nice to have them thought out.
Sometimes, I have to outline. For Teen Author (which was my 2012 NaNo book, for those who are wondering), I kept a detailed page in my Notes app about future chapters, symbolism in the book, and what I researched. For one of my current projects, it's heavily based off of my life at the moment, so I just make sure I have access to diary entries during the time I'm working on and I always have friends I can turn to. There are also a LOT of characters in that story (most minor but all important), so I pulled my old white board off the schoolroom wall and brought it upstairs. Currently, it holds the character web. In the center is my protagonist. Then all around her name are the other characters. Lines connect those who are friends, love interests, and siblings. See the picture below.
About this point, I start feverishly working on the book. I'll try to write a little bit every day until I know it's done. I've never had a moment where I'm uncertain if the story is finished. I don't always know the middle details, but 99.9% of the time, I know at least the general details of what the resolution should be.
Editing. I usually edit as I go just because it's in my nature. I cut back on this a bit during NaNoWriMo, but it's pretty hard to not reread and change things. But after the book is completely done, I'll shove it aside for awhile (I didn't look at Teen Author from February to May). Then I'll go over it and try to catch grammatical and spelling errors while fixing phrasing and changing content.
Next, I submit it to my beta readers. Currently, I only have one reliable one. (Shout-out to Hannah!) I asked two other non-writer friends to critique Teen Author, too. That was back in June. Neither has sent me their critique yet. (You know who you are.)
The last step. Eventually, I want to start querying Teen Author. Or maybe I'll realize how terrible it is and wait until I finish one of my current projects to begin querying. Who knows?