There is so much excellent advice about the drafting process in the world, and I won't pretend to have read all the books and essays that cover the topic, but my favorite of those I have read is Anne Lamott's Bird by Bird. If you've studied the craft of writing for five minutes and haven't heard of this book, it's possible that you are dead and have been for some time. It's wonderful. Arguably the most important chapter is the first, titled "Shitty First Drafts" (but read the rest of it, too). This is a much loved, very popular chapter, and for good reason. Did I mention that it's wonderful? It's wonderful.
I won't bore you by reiterating everything Lamott says in the chapter, but I want to build on her main point in order to share a piece of my own advice.
Lamott's purpose in talking about "shitty first drafts" is not to encourage bad writing. It's to discourage premature editing. AKA: revising before you should.
Let's say you spend two hours writing the first draft of your first chapter for a brand new project. You read it back, and you start to think the writing isn't very good. So, you spend another two hours, maybe three, revising the chapter so that it's like Goldilocks' third choice: juuuust right.
You should feel accomplished and proud, right? Not so fast.
Let me explain what happens to people who apply this approach to a novel-length project.
You're writing along, revising as you go, making good progress, but suddenly come to a point where something big changes, affecting the whole project. The character you thought was a lawyer is actually a high school dropout living in her parents' basement. Oops. Being a perfectionist, you can't just leave the first draft with such a glaring inconsistency, right? What about all those early chapters where you wrote about the character's lofty Manhattan apartment? What about the trouble she was having with her latest client? Guess you need to go back and change those chapters, eh? So you follow the pattern you've set for yourself. You start to revise. You revise and revise, editing as you go, and you reach the point where you got stuck, and you progress past it and feel pretty good, but then, suddenly, something else changes. The main character isn't the woman living in the basement. It's the woman's mother. Well. What about all those chapters written from the daughter's perspective? Guess you need to go back and...
Okay, you get it. The point is, you get stuck in a loop if you take this approach. Eventually, you'll get so frustrated thinking that your project "isn't working" that you throw in the towel. But the project isn't the problem. Your process is.
Here's the thing. Stories change as we write them. That's true for all writers who aren't robots. You cannot get hung up on making the first draft perfect. What you must do is understand the purpose of the draft.
Let's go back to our scenario. The bad news here is that the time you spent editing was a total waste. Throw it right out the window. You might as well have been sleeping. Now you're depressed and questioning your very existence. But hang on. There's good news. All that time you spent writing the chapter? That time was not wasted. See, the writing is what led you to the character and the story as they were meant to be. Through the writing, you discovered the Who and the What: who is this character, and what happens in this story. That's what the first draft is about. It's not about perfect continuity. It's not about pacing. And it's certainly not about writing beautiful sentences. All that comes later.
If you keep this in mind as you attack the first draft, you'll be more comfortable playing it loose, which just might keep you sane, at least for a little while longer.
One last note. Don't make the mistake of treating the first draft like an outline. Outline, plan, pre-write, and outline again, then tackle the first draft. You will still discover things that your outline couldn't predict.