Overwriting is not, in and of itself, a bad thing. Yes, it’s bad if it’s still present in a completed novel, and it’s bad if the writer is incapable of recognizing it, but it can actually serve a purpose in early drafts.
I always think of the first draft (and sometimes the second and third and fourth, depending on how badly I messed up the first) as telling the story to myself. It’s not really meant to be seen by other people (except maybe especially patient CPs who are willing to help me work out major plot kinks). It is meant to help me figure things out.
By ‘things’, of course, I don’t just mean the plot. The first draft is also for exploring characters and the world they inhabit, because yes, worldbuilding is necessary even in non-SFF novels – after all, not everyone lives in the town or city in which your book is set. And this is where many people get caught up in overwriting. There are certain details about your world or your characters that are absolutely vital to the story. There are a lot of details that are really, truly not no matter how much you may love them or how interesting you think they are.
Sometimes it can be hard to figure out which details are which, particularly if you attempt to sort them out before you start writing. I, for one, consistently find around Chapter Three that Detail B really was important and should have been included early on, and then around Chapter Fifteen that Detail A wasn’t as vital as I’d thought it was. While it would be nice to have determined all that before I started writing, I usually can’t.
But you know what? That’s okay. That’s what first drafts are for.
So what’s my point? Don’t worry about your first (or second or third or fourth) draft being neat and tidy. Don’t worry about the fact that you’re 15000 words over your predetermined count or that your first ten pages are all scene-setting or that you’ve written a prologue you know is completely unnecessary.
That stuff is important. That stuff helps you to flesh out a world, to figure out which details will make it feel real to the reader, to determine what’s necessary for your reader to understand and what’s just interesting background fluff. That stuff is what will make your story come alive in later drafts, even if it’s no longer on the page.
So overwrite. Indulge the impulse to spend an entire chapter in one character’s head. Spend a couple of pages meandering through the streets of your setting.
Just remember to cut some of it before your final draft.