Free-writing is about writing to learn and explore. It's not something we do when we already have figured out out precisely what we will write about.
Write without an image of how the finished piece should like.
Word choices, spelling, grammar. None of these matter in this mode because thes are conventions to help us deliver a polished piece at the end. When we're free-writing we haven't committed to anything yet. We have some inclination towards a topic and an idea, but that's it. No point in worrying about whether this is going to be the four hour X for Y people or millineal crime and punishment yet. Believing that we know what we want to say before we actually do will only make us unable to finish down the line and run into what most people call writer's block.
Write whatever flows most naturally.
We often read how disciplined our favorite writers are when finishing a book. These anecdotes are scoped to the later stages of a project when they've long figured out the core-message and are simply materializing and polishing it. If we're free-writing then we require a different form of discipline than what we've always learned about.
In the later stages of a project we need to have discipline of focus. Staying true to the core-message and not getting distracted with tangents or even other projects. In the early stage we need need not discipline of focus but rather the discipline of curiosity. We simply need to be persistent and show up, face the page, and not allow pre-mature images of how our work should be get in the way of our writing. Discipline of curiosity here means not taking ourselves too serious and allowing whatever comes to mind come on the page.
In the later stages of a project we need to have discipline of focus. Staying true to the core-message and not getting distracted with tangents or even other projects. In the early stage we need need not discipline of focus but rather the discipline of curiosity. We simply need to be persistent and show up, face the page, and not allow pre-mature images of how our work should be get in the way of our writing. Discipline of curiosity here means not taking ourselves too serious and allowing whatever comes to mind come on the page.
Write to challenge our beliefs.
Writing is one of the most direct paths to sharpening our thoughts and beliefs. It's easy to allow an idea to tumble in our head for years without challenging it. When we do this the idea can feel so true and bulletproof. But it's when we try putting it down into words that it's revealed how vague of a grasp on the idea we actually have. If we prematurely jump into scoped-writing (writing-to-finished-piece) assuming we know what our core-message is we rob ourselves of the opportunity to not only get a clearer grasp of what we value, but also to learn and form new ones through the process.
Like let's say you knew you wanted to write about sleep and time management... but not sure what you were willing to commit a year to. Then free-writing would help you figure that thing out before you do the 'actual-writing'. The former is more a conversation with yourself than it is writing.