Last week, I offered a few of my big, important rules of writing. I led with those because they are the ones I tend to talk about the most and reinforce in workshops and writing groups. They covered the range from grammar to structure to editing, but they were far from the only rules I swear by. This set is simpler to work with but no less important. The only real difference about these is that I use them less often just because the opportunity does not present itself as often. And on that note...
Edit with purpose. It's an easy trap to fall into - thinking that "editing" a manuscript is just reading it for mistakes, errors, weak writing, or some other failing. You can edit that way, but you mostly gather the low-hanging fruit and miss the real important stuff. "Editing with purpose" is going through your work with a mission, and everything you read should target that one objective. Simple missions can be, "Does this contribute to the plot development?" "Is this character necessary?" or "Does this reinforce the particular mood?" It's easy to read a scene and enjoy a joke you wrote, but overlook the fact that the joke is in the wrong place or might even be a distraction. Editing with a mission tells you when you are on target, or when you might be wandering off-subject.
At some point, trim the fat. As we learn our craft, we get used to trimming off the excess. However, sometimes it helps us to deliberately do a pass through our document and target specific, often unnecessary, words. How many times do we use "that" when we don't need it? What about the entire problem with the passive voice? How about those evil time-killers like "almost," kind of," "sort of," and so forth - the cheap terms that take the strength from our writing? Just do a Find/Replace search with Microsoft Word and do a count for how many of those little monsters are in there, then see if they're necessary. (Spoiler: Most of them aren't.)
Give yourself a timeout. When you create something - especially a larger work - it's important to reward yourself for finishing that ever-important first draft. The best reward you can give yourself is a little time where you don't look at any of it. Put it on a shelf for a while. Some people just need a week, others take a month off. The important part, however, is to let yourself get out of the deep immersion into the story so you can read it with an open mind and a fresh set of eyes. Another benefit, of course, is to just have the full realization of what you've accomplished, which is no small thing. Once the rush is over, you're ready for the hard work.
At some point, it's as finished as it's going to be. When my father painted, he would occasionally get obsessed with some particular aspect of his work to the point where he would get stuck in a loop of reworking and redesigning. However, at some point, he decided the work was finished, he coated it with lacquer, and it was sealed forever. Your writing should be the same way. It will never be perfect. There will always be a stupid error, an opportunity to flesh out characters just a little more, or one more plot twist to add. However, continually changing things is the road to madness, so at some point you have to put the brush down and say, "I'm done." Then take pride in that moment - again, you've earned it.