Nearly everyone gets it wrong.
Yes, ignore spelling, punctuation, grammar in your first draft.
But also ignore everything you know about writing except this: tell your story.
The primary purpose of writing without stopping, spewing an unrefined first draft, is to not give yourself time to edit, even to think.
Only time to feel.
Getting the story down in one shot means leaving the emotions in that we normally selfconsciously or unconsciously edit out if we write slow enough to do so.
As soon as you know your story, any part of it, write it down, quick as you can.
When you know more, write more.
When something changes, change it.
Time enough later to clear up inconsistencies, organize the timeline, refine character and dialogue, polish scenes.
Your first draft may be your only chance to get enough real emotion into your story. And without real emotion, nothing you engineer will be as good.
(Also, the faster you write, the less aware you are of Resistance. A story already told is slightly less subject to its assault.)