Editing. Man, it's a process. For our editing, we take several passes at the same stuff, after our initial writing process is finished.
We take turns most of the time, just going over something again, and making minor edits, or leaving notes for things we want to discuss together. Sometimes there are tiny changes, only a word here or there, other times there are entire passages one or the other of us wants to kill or completely alter.
It's gone over once, twice...and it keeps going! Then our editor takes a look, and we pick at other edits here and there if they're small, or wind up rewriting whole sections. The image here is just one very small example of how much actual editing happens. It's a page from the second book in The Witch Lake Chronicles.
Keep in mind, every color change is an edit that was done on a different day at a different time, by three different people. That isn't even finished up! When we're finally finished, we all take turns getting to turn the chapter all back to black text. It's quite the sense of accomplishment, when you see all those colors disappear, to a solid, edited chapter.