When I first started writing novels, I didn't edit them. I just wrote, and whatever hit the page seemed so wonderful to me that I wouldn't touch it. Having to use white-out on my typed pages may have contributed; I can't stand the smell of the stuff. But I was also a kid, and like all kids I was too wrapped up in the wonder of creating my little gems to consider polishing them.
I've had no formal education as a writer, so reading other writers' books was the way that I learned my work wasn't anywhere near professional quality. Through comparisons, I began to see where I was dropping the ball, and how I could do it differently. Happily I never got into the habit of sporadic, free-for-all editing during the writing process. I would write something, and only when it was finished would I mess with it.
I believe editing styles and methods can be as individual as the writing side of things. I am also not a believer in endless editing; I think it can lead to way too much second-guessing and getting caught in rewriting loops. So the usual disclaimer: of what follows, try it to see if it works for you; if it doesn't, try something else.
The first part of my editing process is what I mentioned during the writing phase: each evening I do a light edit on the new material I've written that day. This is very quick, one-shot editing. I read through the work on screen, and make word, phrase and placement changes as I go along. Mentally I'm still in the writing mindset: I'm not hating the work, or myself, or poisoning everything with doubt; I'm just cleaning it up.
I do a final spelling and grammar check, make those changes, save the edited file, and I'm done. I won't read or edit that portion of the book again until the entire novel is finished. Yes, this takes a certain amount of self-discipline and the temptation to back read and re-edit is always there. Some people enjoy doing that; it seems to serve as a reassurance to them. I'm too impatient to keep doing things over; I want to reach the finish line.
Once I've written a complete first draft of a novel, as with polishing a proposal, I try to put a little time and distance between me and the manuscript. Six months away from it would be ideal, but I don't have that luxury anymore. Generally I take two or three days off from working on it. When I'm ready, I print out a hard copy of the manuscript, grab a highlighter and a red ink pen, find a quiet, comfortable spot, and start the final read-through and edit phase.
I read through the manuscript one time, using the highlighter as I go to slash words, sentences, paragraphs and whole pages. I highlight typos, grammatical errors, repeated words, poor word choices, things I find myself skimming through versus reading, and things that for whatever reason don't hit me the right way. I also look at things more intangible -- am I getting too wordy, not wordy enough, how's my flow, have I been consistent, is my voice in this genre coming through, that sort of thing.
This is the stage when I finally let myself get emotional about the work. I release my internal editor, and take it from me, that bitch is nasty, demanding, and merciless. She decides if I've captured my vision of this story. She jumps on my trouble areas (writing description and emotion give me the most trouble, and I know I tend to skimp or skip in both areas, so my internal editor looks for that.) If she hates something, I slash it with the highlighter. If she really hates something, I line through it with the red pen.
When the internal editor and I are done the first pass, she goes away and I take a break for at least twelve hours. I shift back into writer mode, and think about the major changes and how I want to handle them. I kick myself a few times, and then I let it go. I do try to learn something from each edit -- as in, how can I avoid that problem with the next book I write?
When I go back to the manuscript, I start correcting things. Small corrections I make on the page, major changes I'll rewrite from scratch. I do this mainly on the hard copy, but I will type up large sections of revised work on the computer and clip the new pages to the old ones.
When the hard copy corrections are complete, I do a type-in to revise the manuscript file, print that out, and do a final read-through. I used to do this on the computer, but I wear trifocals now and paper is a bit easier on my eyes. The final read-through is just for typos or errors the revisions may have caused, so this one is light, like my daily new material edit.
When the final read-through is finished, I do the last type-in, print out the novel manuscript, and box it up to ship it out.