Time to lift the hood on my work habits a little. The second draft process for one of my books — Always Outnumbered, Never Outgunned in particular, which is the one I'm currently rewriting — works something like this.
Before anything else, I go chapter-by-chapter and scene-by-scene through the book and create what I call a "map" — a quick outline written from the first draft that describes what each scene is, what it tries to accomplish. The reason for doing this is to give myself a 30,000-foot view of the book as it actually is in its current state, as opposed to the outline I worked from when I was first writing it.
The other reason for this is to give myself some idea of where to deal with all the issues I noted down in under the heading of "Things to do in the next draft". If I know there's some general issue, it helps to know what specific places in the book I could use to address it.
I poked briefly through the "things to do" file and found a lot of stuff that is either redundant or obsolete. Some things seem like they're going to be these big, potentially seismic issues, and then turn out to be almost totally irrelevant to anything the story needs to be about. Other things, you blink and miss them, and they end up being crucial. But it doesn't hurt to write it all down and figure out later what of it matters.
One of the bits of personal discipline you have to develop when doing all this is to figure out how to know if something is in fact important or not. When you're in the thick of writing a story, everything seems important, because you have no idea if any one thing is or isn't going to add up to something until the moment when you're actually typing THE END. And even then, as I've found, you can develop attachments to things — you can overstate to yourself the importance they actually have.
I've long suspected this is part of why some books turn into these thousand-page deforestation exercises. Some things just need to be left out of the picture, but the author can't do it — everything has to have its day. It's a temptation I've known more than a few times, and it usually comes in the form of feeling like you're not doing justice to the full measure of what your story is about. How this little angle and this particular insight need to be there so that that aspect of the character is fully detailed ... and you never get out of the rabbit hole. Writing, like cinema, is a matter of both what's in the frame and out.