I often think of writing a book in terms of decorating a house. I touched on this idea the other day with the post about making each scene sing. This post is about a similar way of looking at your work.
At the start, you decide to write a book and you assemble your ideas. Deciding to do this is akin to buying a new house. It's big, it's empty and there's lots of room. You may sketch out ideas for this or that area of the house (parts of the book). Even before you move in (start the book) you've got it all planned out.
Finally, you move your stuff (your ideas) there and decorate the rooms (write the scenes). Whether it's a book or a house, it's time to dress the place. After all, you've bought it.
Each room is a scene. What will you place there? What personality or story will the room (scene) contain? Just as you try things out in a real room, putting this here and hanging that there to get a sense of the room's potential, you can write a scene a certain way and see how it sounds. With both the room decoration and the scene, we have the option to come back later and improve it, bit by bit.
So you store the information (save your file) and move on to another room. At least you've staked your claim on the former room; you'll get back to it later. For now, you want to spread your efforts throughout the house, to give it a sense of style. You decorate a room to a certain extent and then move on to the next room. In this sense, you write a scene and know that another scene is necessary -- you move on.
At some point, you've laid down a framework of your style throughout the house. That's the first draft. Now you can go back and purchase (write) the things each room really needs. (Make the scene sing.) And just like filling a room with guests at a party, you place your characters strategically throughout the house and watch (and write about) their interplay.
When you've written the book and you like what you've done, you move on to the outside of the house (the book cover) and do what you can to make the place attractive and inviting, so people will come to visit.
And finally you have a party and invite people to your finished house (launch and sell the book). It works for me.